Index: build/premake/extern_libs5.lua
===================================================================
--- build/premake/extern_libs5.lua
+++ build/premake/extern_libs5.lua
@@ -626,14 +626,14 @@
 				end
 			else
 				filter { "Debug", "action:vs*" }
-					links { "mozjs78-ps-debug" }
-					links { "mozjs78-ps-rust-debug" }
+					links { "mozjs91-ps-debug" }
+					links { "mozjs91-ps-rust-debug" }
 				filter { "Debug", "action:not vs*" }
-					links { "mozjs78-ps-debug" }
-					links { "mozjs78-ps-rust" }
+					links { "mozjs91-ps-debug" }
+					links { "mozjs91-ps-rust" }
 				filter { "Release" }
-					links { "mozjs78-ps-release" }
-					links { "mozjs78-ps-rust" }
+					links { "mozjs91-ps-release" }
+					links { "mozjs91-ps-rust" }
 				filter { }
 				add_source_lib_paths("spidermonkey")
 			end
Index: libraries/source/spidermonkey/FixFpNormIssue.diff
===================================================================
--- /dev/null
+++ libraries/source/spidermonkey/FixFpNormIssue.diff
@@ -0,0 +1,110 @@
+--- a/modules/fdlibm/src/math_private.h
++++ b/modules/fdlibm/src/math_private.h
+@@ -30,8 +30,13 @@
+  * Adapted from https://github.com/freebsd/freebsd-src/search?q=__double_t
+  */
+ 
++#if defined __FLT_EVAL_METHOD__ && (__FLT_EVAL_METHOD__ == 2)
++typedef long double      __double_t;
++#else
+ typedef double      __double_t;
++#endif
+ typedef __double_t  double_t;
++typedef float   __float_t;
+ 
+ /*
+  * The original fdlibm code used statements like:
+@@ -630,6 +634,53 @@
+ 	return ((double)(x + 0x1.8p52) - 0x1.8p52);
+ }
+ 
++static inline float
++rnintf(__float_t x)
++{
++	/*
++	 * As for rnint(), except we could just call that to handle the
++	 * extra precision case, usually without losing efficiency.
++	 */
++	return ((float)(x + 0x1.8p23F) - 0x1.8p23F);
++}
++
++#ifdef LDBL_MANT_DIG
++/*
++ * The complications for extra precision are smaller for rnintl() since it
++ * can safely assume that the rounding precision has been increased from
++ * its default to FP_PE on x86.  We don't exploit that here to get small
++ * optimizations from limiting the rangle to double.  We just need it for
++ * the magic number to work with long doubles.  ld128 callers should use
++ * rnint() instead of this if possible.  ld80 callers should prefer
++ * rnintl() since for amd64 this avoids swapping the register set, while
++ * for i386 it makes no difference (assuming FP_PE), and for other arches
++ * it makes little difference.
++ */
++
++static inline long double
++rnintl(long double x)
++{
++  /* The WRAPPED__CONCAT() macro below is required for non-FreeBSD targets
++     which don't have a multi-level CONCAT macro implementation. On those
++     targets the hexadecimal floating-point values being created don't expand
++     properly resulting in code that cannot be compiled.
++
++     The extra level provided by this macro should not affect FreeBSD, should
++     this code be used there.
++
++     See the following for more details:
++
++       https://gcc.gnu.org/onlinedocs/gcc-3.0.1/cpp_3.html#SEC32
++       https://sources.debian.org/src/glibc/2.32-3/misc/sys/cdefs.h/
++       https://github.com/freebsd/freebsd-src/blob/main/sys/sys/cdefs.h
++  */
++	#define WRAPPED__CONCAT(x,y) __CONCAT(x,y)
++
++	return (x + WRAPPED__CONCAT(0x1.8p, LDBL_MANT_DIG) / 2 -
++		WRAPPED__CONCAT(0x1.8p, LDBL_MANT_DIG) / 2);
++}
++#endif /* LDBL_MANT_DIG */
++
+ /*
+  * irint() and i64rint() give the same result as casting to their integer
+  * return type provided their arg is a floating point integer.  They can
+@@ -646,6 +697,39 @@
+ #define	irint(x)	((int)(x))
+ #endif
+ 
++#define	i64rint(x)	((int64_t)(x))	/* only needed for ld128 so not opt. */
++
++#if defined(__i386__) && defined(__GNUCLIKE_ASM)
++static __inline int
++irintf(float x)
++{
++	int n;
++
++	__asm("fistl %0" : "=m" (n) : "t" (x));
++	return (n);
++}
++
++static __inline int
++irintd(double x)
++{
++	int n;
++
++	__asm("fistl %0" : "=m" (n) : "t" (x));
++	return (n);
++}
++#endif
++
++#if (defined(__amd64__) || defined(__i386__)) && defined(__GNUCLIKE_ASM)
++static __inline int
++irintl(long double x)
++{
++	int n;
++
++	__asm("fistl %0" : "=m" (n) : "t" (x));
++	return (n);
++}
++#endif
++
+ #ifdef DEBUG
+ #if defined(__amd64__) || defined(__i386__)
+ #define	breakpoint()	asm("int $3")
Index: libraries/source/spidermonkey/FixMozglue.diff
===================================================================
--- libraries/source/spidermonkey/FixMozglue.diff
+++ libraries/source/spidermonkey/FixMozglue.diff
@@ -1,47 +1,16 @@
-diff --git a/js/src/build/moz.build b/js/src/build/moz.build
-index b311e9549fed..55f26497ec8d 100644
---- a/js/src/build/moz.build
-+++ b/js/src/build/moz.build
-@@ -10,9 +10,7 @@ CONFIGURE_SUBST_FILES += [
- ]
- 
- LIBRARY_DEFINES['EXPORT_JS_API'] = True
--
--if not CONFIG['JS_STANDALONE']:
--    LIBRARY_DEFINES['MOZ_HAS_MOZGLUE'] = True
-+LIBRARY_DEFINES['MOZ_HAS_MOZGLUE'] = True
- 
- # JavaScript must be built shared, even for static builds, as it is used by
- # other modules which are always built shared. Failure to do so results in
-diff --git a/mozglue/build/moz.build b/mozglue/build/moz.build
-index ab0cff86fafc..d8bcead49deb 100644
---- a/mozglue/build/moz.build
-+++ b/mozglue/build/moz.build
-@@ -9,6 +9,7 @@
- # If this is ever changed, update MOZ_SHARED_MOZGLUE in browser/installer/Makefile.in
- if CONFIG['JS_STANDALONE'] and not CONFIG['MOZ_MEMORY']:
-     Library('mozglue')
-+    FINAL_LIBRARY = 'js'
- elif CONFIG['OS_TARGET'] in ('WINNT', 'Darwin', 'Android'):
-     SharedLibrary('mozglue')
- else:
-diff --git a/config/makefiles/target_binaries.mk b/config/makefiles/target_binaries.mk
-index 31b2c4367e94..a7f9037dfd54 100644
-diff --git a/js/src/moz.build b/js/src/moz.build
-index 9c2ab1e1ac18..7444259bca6a 100755
 --- a/js/src/moz.build
 +++ b/js/src/moz.build
-@@ -50,7 +50,12 @@ with Files('builtin/intl/*'):
- if CONFIG['ENABLE_WASM_CRANELIFT']:
-     CONFIGURE_SUBST_FILES += ['rust/extra-bindgen-flags']
+@@ -50,9 +50,12 @@
+ if CONFIG["ENABLE_WASM_CRANELIFT"]:
+     CONFIGURE_SUBST_FILES += ["rust/extra-bindgen-flags"]
  
--if not CONFIG['JS_DISABLE_SHELL']:
-+if CONFIG['JS_STANDALONE'] and CONFIG['JS_DISABLE_SHELL']:
-+    DIRS += [
-+        'rust',
-+    ]
++DIRS += [
++    "rust"
++]
 +
-+elif not CONFIG['JS_DISABLE_SHELL']:
+ if not CONFIG["JS_DISABLE_SHELL"]:
      DIRS += [
-         'rust',
-         'shell',
+-        "rust",
+         "shell",
+     ]
+ 
Index: libraries/source/spidermonkey/FixRustLinkage.diff
===================================================================
--- /dev/null
+++ libraries/source/spidermonkey/FixRustLinkage.diff
@@ -0,0 +1,16 @@
+--- a/js/src/moz.build
++++ b/js/src/moz.build
+@@ -50,9 +50,12 @@
+ if CONFIG["ENABLE_WASM_CRANELIFT"]:
+     CONFIGURE_SUBST_FILES += ["rust/extra-bindgen-flags"]
+ 
++DIRS += [
++    "rust"
++]
++
+ if not CONFIG["JS_DISABLE_SHELL"]:
+     DIRS += [
+-        "rust",
+         "shell",
+     ]
+ 
Index: libraries/source/spidermonkey/FixVirtualEnv.diff
===================================================================
--- libraries/source/spidermonkey/FixVirtualEnv.diff
+++ libraries/source/spidermonkey/FixVirtualEnv.diff
@@ -1,20 +1,16 @@
 --- a/python/mozbuild/mozbuild/virtualenv.py
 +++ b/python/mozbuild/mozbuild/virtualenv.py
-@@ -235,7 +235,7 @@
-         if os.path.islink(venv_python):
-             os.remove(venv_python)
+@@ -246,11 +246,12 @@
+         if os.path.exists(self.virtualenv_root):
+             shutil.rmtree(self.virtualenv_root)
  
--        args = [python, self.virtualenv_script_path,
-+        args = [python, "-m" "virtualenv",
-                 # Without this, virtualenv.py may attempt to contact the outside
-                 # world and search for or download a newer version of pip,
-                 # setuptools, or wheel. This is bad for security, reproducibility,
-@@ -438,7 +438,7 @@
-                 handle_package(package)
- 
-             sitecustomize = os.path.join(
--                os.path.dirname(os.__file__), 'sitecustomize.py')
-+                os.path.dirname(sys.executable), 'sitecustomize.py')
-             with open(sitecustomize, 'w') as f:
-                 f.write(
-                     '# Importing mach_bootstrap has the side effect of\n'
+         args = [
+             python,
+-            self.virtualenv_script_path,
++            "-m",
++            "virtualenv",
+             # Without this, virtualenv.py may attempt to contact the outside
+             # world and search for or download a newer version of pip,
+             # setuptools, or wheel. This is bad for security, reproducibility,
+             # and speed.
+             "--no-download",
Index: libraries/source/spidermonkey/FixWindowsLibNames.diff
===================================================================
--- /dev/null
+++ libraries/source/spidermonkey/FixWindowsLibNames.diff
@@ -0,0 +1,16 @@
+--- a/js/src/old-configure
++++ b/js/src/old-configure
+@@ -7035,10 +7035,10 @@
+ 
+ 
+ 
+-if test -n "$JS_STANDALONE"; then
+-JS_LIBRARY_NAME="mozjs-$MOZILLA_SYMBOLVERSION"
++if test -n "$MOZ_DEBUG"; then
++JS_LIBRARY_NAME="mozjs$MOZILLA_SYMBOLVERSION-ps-debug"
+ else
+-JS_LIBRARY_NAME="mozjs"
++JS_LIBRARY_NAME="mozjs$MOZILLA_SYMBOLVERSION-ps-release"
+ fi
+ JS_CONFIG_LIBS="$NSPR_LIBS $LIBS"
+ if test -n "$GNU_CC"; then
Index: libraries/source/spidermonkey/README.txt
===================================================================
--- libraries/source/spidermonkey/README.txt
+++ libraries/source/spidermonkey/README.txt
@@ -28,16 +28,20 @@
 We provide precompiled binaries for Windows.
 If you still need to build on Windows, here's a short guide.
 
-The basic idea is to follow the instructions to build Firefox:
-https://firefox-source-docs.mozilla.org/setup/windows_build.html#mozillabuild
-And after running "mach boostrap", run ./build.sh
+In the Visual Studio Installer:
+- Install Clang, Clang-CL
 
-The customised option (which I used):
-- Install mozilla-build per the instructions above
-- Install rust (make sure to add it to your PATH)
-- Open Powershell and run "rustup install i686-pc-windows-msvc" and "rustup install x86_64-pc-windows-msvc"
-- Install LLVM 8 prebuilt binaries from https://releases.llvm.org somewhere.
-- From powershell, run ". C:/mozilla-build/start-shell.bat", cd to 0ad/libraries/source/spidermonkey and then run "./build.sh"
-- This will fail. Edit build.sh to not rebuild (REBUILD=false)
-- Edit the build/moz.configure/toolchain.configure file to have your LLVM/bin folder in the `toolchain_search_path`. I added the path directly to the bootstrapped variable L721
-- Rerun build.sh. It should run.
+Install Rust from the official website.
+
+Download & install Mozilla Build from [here](https://ftp.mozilla.org/pub/mozilla/libraries/win32/MozillaBuildSetup-Latest.exe).
+In Mozilla build run:
+rustup target add i686-pc-windows-msvc
+rustup target add x86_64-pc-windows-msvc
+
+From powershell, run the following commands.
+They will start a mozbuild shell, setup LLVM_LOCATION (may vary),
+then run the build.
+. C:/mozilla-build/start-shell.bat
+LLVM_LOCATION="/c/PROGRA~1/MICROS~1/2017/Community/VC/Tools/Llvm/x64/bin/"
+export PATH="$PATH:$LLVM_LOCATION"
+cd "/libraries/source/spidermonkey" &&".\build.sh"
Index: libraries/source/spidermonkey/build.sh
===================================================================
--- libraries/source/spidermonkey/build.sh
+++ libraries/source/spidermonkey/build.sh
@@ -3,10 +3,10 @@
 set -e
 
 # This should match the version in config/milestone.txt
-FOLDER="mozjs-78.6.0"
+FOLDER="mozjs-91.13.1"
 # If same-version changes are needed, increment this.
-LIB_VERSION="78.6.0+3"
-LIB_NAME="mozjs78-ps"
+LIB_VERSION="91.13.1+0"
+LIB_NAME="mozjs91-ps"
 
 # Since this script is called by update-workspaces.sh, we want to quickly
 # avoid doing any work if SpiderMonkey is already built and up-to-date.
@@ -21,6 +21,8 @@
 echo "Building SpiderMonkey..."
 echo
 
+OS="${OS:=$(uname -s)}"
+
 # Use Mozilla make on Windows
 if [ "${OS}" = "Windows_NT" ]
 then
@@ -33,6 +35,7 @@
 
 # Standalone SpiderMonkey can not use jemalloc (see https://bugzilla.mozilla.org/show_bug.cgi?id=1465038)
 # Jitspew doesn't compile on VS17 in the zydis disassembler - since we don't use it, deactivate it.
+# Trace-logging doesn't compile for now.
 CONF_OPTS="--disable-tests
            --disable-jemalloc
            --disable-js-shell
@@ -40,25 +43,31 @@
            --enable-shared-js
            --disable-jitspew"
 
+if [ -n "$PROFILE" ]
+then
+  CONF_OPTS="$CONF_OPTS --enable-profiling
+                        --enable-perf
+                        --enable-instruments
+                        --enable-jitspew
+                        --with-jitreport-granularity=3"
+fi
+
 if [ "${OS}" = "Windows_NT" ]
 then
   CONF_OPTS="${CONF_OPTS} --with-visual-studio-version=2017 --target=i686"
-else
-  CONF_OPTS="${CONF_OPTS}"
-fi
-
-if [ "`uname -s`" = "Darwin" ]
-then
-  ARCH=${ARCH:=""}
+elif [ "${OS}" = "Darwin" ]
+  then
+  # Unless we are forcing an architecture, switch between ARM / x86 based on platform.
   if [ -z "${ARCH}" ]; then
-    if [ "`uname -m`" == "arm64" ]; then
+    if [ "$(uname -m)" == "arm64" ]
+    then
       ARCH="aarch64"
     else
       ARCH="x86_64"
     fi
-  elif [ $ARCH == "arm64"  ]; then
-    # SM78 doesn't know about arm64 yet, and that's passed by build-osx-libs.sh, so fix it explicitly.
-    ARCH="aarch64"
+  #elif [ $ARCH == "arm64"  ]; then
+  #  # SM78 doesn't know about arm64 yet, and that's passed by build-osx-libs.sh, so fix it explicitly.
+  #  ARCH="aarch64"
   fi
   CONF_OPTS="${CONF_OPTS} --target=$ARCH-apple-darwin"
 
@@ -80,8 +89,8 @@
 # (Don't run this on windows as it would likely fail spuriously)
 if [ "${OS}" != "Windows_NT" ]
 then
-  [ ! -z "$(command -v rustc)" ] || (echo "Error: rustc is not available. Install the rust toolchain (rust + cargo) before proceeding." && exit 1)
-  [ ! -z "${LLVM_OBJDUMP}" ] || (echo "Error: LLVM objdump is not available. Install it (likely via LLVM-clang) before proceeding." && exit 1)
+  [ -n "$(command -v rustc)" ] || (echo "Error: rustc is not available. Install the rust toolchain (rust + cargo) before proceeding." && exit 1)
+  [ -n "${LLVM_OBJDUMP}" ] || (echo "Error: LLVM objdump is not available. Install it (likely via LLVM-clang) before proceeding." && exit 1)
 fi
 
 # If Valgrind looks like it's installed, then set up SM to support it
@@ -101,41 +110,40 @@
 
 # It can occasionally be useful to not rebuild everything, but don't do this by default.
 REBUILD=${REBUILD:=true}
-if $REBUILD = true;
+if [ $REBUILD = true ]
 then
   # Delete the existing directory to avoid conflicts and extract the tarball
   rm -rf "$FOLDER"
-  if [ ! -e "${FOLDER}.tar.bz2" ];
+  if [ ! -e "${FOLDER}.tar.xz" ]
   then
     # The tarball is committed to svn, but it's useful to let jenkins download it (when testing upgrade scripts).
-    download="$(command -v wget || echo "curl -L -o "${FOLDER}.tar.bz2"")"
-    $download "https://github.com/wraitii/spidermonkey-tarballs/releases/download/v78.6.0/${FOLDER}.tar.bz2"
+    download="$(command -v wget || echo "curl -L -o "${FOLDER}.tar.xz"")"
+    $download "https://github.com/wraitii/spidermonkey-tarballs/releases/download/${FOLDER}/${FOLDER}.tar.xz"
   fi
-  tar xjf "${FOLDER}.tar.bz2"
+  tar xfJ "${FOLDER}.tar.xz"
 
   # Clean up header files that may be left over by earlier versions of SpiderMonkey
   rm -rf include-unix-debug
   rm -rf include-unix-release
 
-  # Apply patches
   cd "$FOLDER"
-  . ../patch.sh
-  # Copy a more recent autoconf config.guess to handle ARM macs properly.
-  cp -f ../config.guess build/autoconf/
+
   # Prevent complaining that configure is outdated.
   touch ./js/src/configure
+
+  # Apply patches
+  . ../patch.sh
 else
   cd "$FOLDER"
 fi
 
 # Debug version of SM is broken on FreeBSD.
-if [ "$(uname -s)" != "FreeBSD" ]; then
+if [ "${OS}" != "FreeBSD" ]
+then
   mkdir -p build-debug
   cd build-debug
-  # SM configure checks for autoconf, but we don't actually need it.
-  # To avoid a dependency, pass something arbitrary (it does need to be an actual program).
   # llvm-objdump is searched for with the complete name, not simply 'objdump', account for that.
-  CXXFLAGS="${CXXFLAGS}" ../js/src/configure AUTOCONF="ls" \
+  CXXFLAGS="${CXXFLAGS}" ../js/src/configure \
     LLVM_OBJDUMP="${LLVM_OBJDUMP}" \
     ${CONF_OPTS} \
     --enable-debug \
@@ -147,7 +155,7 @@
 
 mkdir -p build-release
 cd build-release
-CXXFLAGS="${CXXFLAGS}" ../js/src/configure AUTOCONF="ls" \
+CXXFLAGS="${CXXFLAGS}" ../js/src/configure \
   LLVM_OBJDUMP="${LLVM_OBJDUMP}" \
   ${CONF_OPTS} \
   --enable-optimize
@@ -169,10 +177,10 @@
   LIB_PREFIX=lib
   LIB_SUFFIX=.so
   STATIC_LIB_SUFFIX=.a
-  if [ "`uname -s`" = "OpenBSD" ];
+  if [ "${OS}" = "OpenBSD" ];
   then
     LIB_SUFFIX=.so.1.0
-  elif [ "`uname -s`" = "Darwin" ];
+  elif [ "${OS}" = "Darwin" ];
   then
     LIB_SUFFIX=.a
   fi
@@ -197,7 +205,7 @@
 mkdir -p "${INCLUDE_DIR_RELEASE}"
 cp -R -L "${FOLDER}"/build-release/dist/include/* "${INCLUDE_DIR_RELEASE}/"
 
-if [ "$(uname -s)" != "FreeBSD" ]; then
+if [ "${OS}" != "FreeBSD" ]; then
   mkdir -p "${INCLUDE_DIR_DEBUG}"
   cp -R -L "${FOLDER}"/build-debug/dist/include/* "${INCLUDE_DIR_DEBUG}/"
 fi
@@ -212,7 +220,7 @@
 rust_path=$(grep jsrust < "${FOLDER}/build-release/js/src/build/backend.mk" | cut -d = -f 2 | cut -c2-)
 cp -L "${rust_path}" "lib/${LIB_PREFIX}${LIB_NAME}-rust${STATIC_LIB_SUFFIX}"
 
-if [ "`uname -s`" = "Darwin" ]
+if [ "${OS}" = "Darwin" ]
 then
   # On MacOS, copy the static libraries only.
   cp -L "${FOLDER}/build-${DEB}/js/src/build/${LIB_PREFIX}js_static${LIB_SUFFIX}" "lib/${LIB_PREFIX}${LIB_NAME}-${DEB}${LIB_SUFFIX}"
@@ -230,15 +238,11 @@
   # Copy the debug jsrust library.
   rust_path=$(grep jsrust < "${FOLDER}/build-debug/js/src/build/backend.mk" | cut -d = -f 2 | cut -c2-)
   cp -L "${rust_path}" "lib/${LIB_PREFIX}${LIB_NAME}-rust-debug${STATIC_LIB_SUFFIX}"
-  # Windows need some additional libraries for posix emulation.
-  cp -L "${FOLDER}/build-release/dist/bin/${LIB_PREFIX}nspr4.dll" "../../../binaries/system/${LIB_PREFIX}nspr4.dll"
-  cp -L "${FOLDER}/build-release/dist/bin/${LIB_PREFIX}plc4.dll" "../../../binaries/system/${LIB_PREFIX}plc4.dll"
-  cp -L "${FOLDER}/build-release/dist/bin/${LIB_PREFIX}plds4.dll" "../../../binaries/system/${LIB_PREFIX}plds4.dll"
 else
   # Copy shared libs to both lib/ and binaries/ so the compiler and executable (resp.) can find them.
   cp -L "${FOLDER}/build-${REL}/js/src/build/${LIB_PREFIX}${LIB_NAME}-${REL}${LIB_SUFFIX}" "lib/${LIB_PREFIX}${LIB_NAME}-${REL}${LIB_SUFFIX}"
   cp -L "${FOLDER}/build-${REL}/js/src/build/${LIB_PREFIX}${LIB_NAME}-${REL}${LIB_SUFFIX}" "../../../binaries/system/${LIB_PREFIX}${LIB_NAME}-${REL}${LIB_SUFFIX}"
-  if [ "$(uname -s)" != "FreeBSD" ]; then
+  if [ "${OS}" != "FreeBSD" ]; then
     cp -L "${FOLDER}/build-${DEB}/js/src/build/${LIB_PREFIX}${LIB_NAME}-${DEB}${LIB_SUFFIX}" "../../../binaries/system/${LIB_PREFIX}${LIB_NAME}-${DEB}${LIB_SUFFIX}"
     cp -L "${FOLDER}/build-${DEB}/js/src/build/${LIB_PREFIX}${LIB_NAME}-${DEB}${LIB_SUFFIX}" "lib/${LIB_PREFIX}${LIB_NAME}-${DEB}${LIB_SUFFIX}"
   fi
Index: libraries/source/spidermonkey/patch.sh
===================================================================
--- libraries/source/spidermonkey/patch.sh
+++ libraries/source/spidermonkey/patch.sh
@@ -1,87 +1,33 @@
 #!/bin/sh
+set -ev
+
 # Apply patches if needed
 # This script gets called from build.sh.
 
-# SM78 fails to create virtual envs on macs with python > 3.7
-# Unfortunately, 3.7 is mostly unavailable on ARM macs.
-# Therefore, replace the custom script with a more up-to-date version from pip
-# if python is detected to be newer than 3.7.
-if [ "$(uname -s)" = "Darwin" ];
-then
-    PYTHON_MINOR_VERSION="$(python3 -c 'import sys; print(sys.version_info.minor)')"
-    if [ "$PYTHON_MINOR_VERSION" -gt 7 ];
-    then
-        # SM actually uses features from the full-fledged virtualenv package
-        # and not just venv, so install it to be safe.
-        # Install it locally to not pollute anything.
-        # Install specifically a version that's know to work.
-        pip3 install --upgrade -t virtualenv 'virtualenv==20.13.1'
-        export PYTHONPATH="$(pwd)/virtualenv:$PYTHONPATH"
-        patch -p1 < ../FixVirtualEnv.diff
-    fi
-else
-    # In python 3.10 `sysconfig._get_default_scheme()` was renamed to
-    # `sysconfig.get_default_scheme()`. This breaks the version of
-    # `virtualenv` bundled with the spidermonkey source code.
-    #
-    # It is assumed that the updated version fetched for macOS systems
-    # above does not have this problem.
-    patch -p1 < ../FixVirtualenvForPython310.diff
-fi
-
-# Mozglue symbols need to be linked against static builds.
+# The rust code is only linked if the JS Shell is enabled,
+# which fails now that rust is required in all cases.
 # https://bugzilla.mozilla.org/show_bug.cgi?id=1588340
-patch -p1 < ../FixMozglue.diff
+patch -p1 < ../FixRustLinkage.diff
 
-# Update library names to have separate debug/release libraries.
-patch -p1 < ../RenameLibs.diff
+# On windows, we need to differente debug/release library names.
+patch -p1 < ../FixWindowsLibNames.diff
 
-# Fix ~SharedArrayRawBufferRefs symbol not found.
-# See https://bugzilla.mozilla.org/show_bug.cgi?id=1644600
-# Many thanks to bellaz89 for finding this and reporting it
-patch -p1 < ../FixSharedArray.diff
-
-# Fix public export on MSVC (C2487)
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1614243
-# (mentionned in the comments, no patch/commit found)
-patch -p1 < ../FixPublicExport.diff
-
-# Fix Rooted<void*> not working on VS17
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1679736
-# (Landed in 85)
-patch -p1 < ../FixMSVCRootedVoid.diff
-
-# Two SDK-related issues.
-# -ftrivial-auto-var-init is clang 8,
-# but apple-clang 10.0.0 (the maximum in 10.13)
-# doesn't actually have it, so patch it out.
-# Secondly, there is a 'max SDK version' in SM,
-# which is set to 10.15.4 in SM78.
-# Upstream has changed this to 10.11 at the moment,
-# so this patches it to an arbitrarily high Mac OS 11
-patch -p1 < ../FixMacBuild.diff
-
-# In python 3.3, the Collections' Abstract Base Classes were moved from `collections` to
-# `collections.abc`, and aliases were set up for backwards compatibility.
-# In python 3.10, these aliases were removed, requiring all code that used them to update.
-patch -p1 < ../FixPythonCollectionABC.diff
-
-# Fix FP access breaking compilation on RPI3+
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1526653
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1536491
-patch -p1 < ../FixRpiUnalignedFpAccess.diff
-
-# Bug 1684261 upstreamed from 78.8: https://hg.mozilla.org/releases/mozilla-esr78/rev/0e8f444683cb
-# Note that this isn't quite the upstream patch to match our version.
-patch -p1 < ../FixRust150.diff
+# There is an issue on 32-bit linux builds sometimes.
+# NB: the patch here is Comment 21 modified by Comment 25
+# but that seems to imperfectly fix the issue with GCC.
+# It also won't compile on windows - in doubt, apply only where relevant.
+# https://bugzilla.mozilla.org/show_bug.cgi?id=1729459
+if [ "$(uname -m)" = "i686" ]
+then
+	patch -p1 < ../FixFpNormIssue.diff
+fi
 
-# Patch those separately, as they might interfere with normal behaviour.
-if [ "$(uname -s)" = "FreeBSD" ];
+if [ "$(uname -s)" = "Darwin" ]
 then
-    # https://svnweb.freebsd.org/ports/head/lang/spidermonkey78/files/patch-js_moz.configure?view=log
-    patch -p1 < ../FixFreeBSDReadlineDetection.diff
-    # https://svnweb.freebsd.org/ports/head/lang/spidermonkey78/files/patch-third__party_rust_cc_.cargo-checksum.json?view=log
-    patch -p1 < ../FixFreeBSDCargoChecksum.diff
-    # https://svnweb.freebsd.org/ports/head/lang/spidermonkey78/files/patch-third__party_rust_cc_src_lib.rs?view=log
-    patch -p1 < ../FixFreeBSDRustThirdPartyOSDetection.diff
+    # The bundled virtualenv version is not working on MacOS
+    # with recent homebrew and needs to be upgraded.
+    # Install it locally to not pollute anything.
+	pip3 install --upgrade -t virtualenv virtualenv
+    export PYTHONPATH="$(pwd)/virtualenv:$PYTHONPATH"
+    patch -p1 < ../FixVirtualenv.diff
 fi
Index: source/gui/Scripting/JSInterface_GUIProxy.h
===================================================================
--- source/gui/Scripting/JSInterface_GUIProxy.h
+++ source/gui/Scripting/JSInterface_GUIProxy.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -170,13 +170,13 @@
 
 	// The JS code will see undefined when querying a property descriptor.
 	virtual bool getOwnPropertyDescriptor(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::HandleId UNUSED(id),
-										  JS::MutableHandle<JS::PropertyDescriptor> UNUSED(desc)) const override
+	                                      JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> UNUSED(desc)) const override
 	{
 		return true;
 	}
 	// Throw an exception is JS code attempts defining a property.
 	virtual bool defineProperty(JSContext* UNUSED(cx), JS::HandleObject UNUSED(proxy), JS::HandleId UNUSED(id),
-								JS::Handle<JS::PropertyDescriptor> UNUSED(desc), JS::ObjectOpResult& UNUSED(result)) const override
+	                            JS::Handle<JS::PropertyDescriptor> UNUSED(desc), JS::ObjectOpResult& UNUSED(result)) const override
 	{
 		return false;
 	}
Index: source/gui/Scripting/JSInterface_GUIProxy_impl.h
===================================================================
--- source/gui/Scripting/JSInterface_GUIProxy_impl.h
+++ source/gui/Scripting/JSInterface_GUIProxy_impl.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -88,7 +88,7 @@
 {
 	if (!obj)
 		return nullptr;
-	if (JS_GetClass(obj) != &JSInterface_GUIProxy::ClassDefinition())
+	if (JS::GetClass(obj) != &JSInterface_GUIProxy::ClassDefinition())
 		return nullptr;
 	return UnsafeFromPrivateSlot<IGUIObject>(obj);
 }
Index: source/scriptinterface/ScriptContext.h
===================================================================
--- source/scriptinterface/ScriptContext.h
+++ source/scriptinterface/ScriptContext.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
Index: source/scriptinterface/ScriptContext.cpp
===================================================================
--- source/scriptinterface/ScriptContext.cpp
+++ source/scriptinterface/ScriptContext.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -107,7 +107,8 @@
 	JS::SetGCSliceCallback(m_cx, GCSliceCallbackHook);
 
 	JS_SetGCParameter(m_cx, JSGC_MAX_BYTES, m_ContextSize);
-	JS_SetGCParameter(m_cx, JSGC_MODE, JSGC_MODE_INCREMENTAL);
+	JS_SetGCParameter(m_cx, JSGC_INCREMENTAL_GC_ENABLED, true);
+	JS_SetGCParameter(m_cx, JSGC_PER_ZONE_GC_ENABLED, false);
 
 	JS_SetOffthreadIonCompilationEnabled(m_cx, true);
 
@@ -143,7 +144,7 @@
 	// Schedule the zone for GC, which will destroy the realm.
 	if (JS::IsIncrementalGCInProgress(m_cx))
 		JS::FinishIncrementalGC(m_cx, JS::GCReason::API);
-	JS::PrepareZoneForGC(js::GetRealmZone(realm));
+	JS::PrepareZoneForGC(m_cx, js::GetRealmZone(realm));
 	m_Realms.remove(realm);
 }
 
@@ -241,7 +242,7 @@
 #endif
 				PrepareZonesForIncrementalGC();
 				if (!JS::IsIncrementalGCInProgress(m_cx))
-					JS::StartIncrementalGC(m_cx, GC_NORMAL, JS::GCReason::API, GCSliceTimeBudget);
+					JS::StartIncrementalGC(m_cx, JS::GCOptions::Normal, JS::GCReason::API, GCSliceTimeBudget);
 				else
 					JS::IncrementalGCSlice(m_cx, JS::GCReason::API, GCSliceTimeBudget);
 			}
@@ -252,14 +253,16 @@
 
 void ScriptContext::ShrinkingGC()
 {
-	JS_SetGCParameter(m_cx, JSGC_MODE, JSGC_MODE_ZONE);
+	JS_SetGCParameter(m_cx, JSGC_INCREMENTAL_GC_ENABLED, false);
+	JS_SetGCParameter(m_cx, JSGC_PER_ZONE_GC_ENABLED, true);
 	JS::PrepareForFullGC(m_cx);
-	JS::NonIncrementalGC(m_cx, GC_SHRINK, JS::GCReason::API);
-	JS_SetGCParameter(m_cx, JSGC_MODE, JSGC_MODE_INCREMENTAL);
+	JS::NonIncrementalGC(m_cx, JS::GCOptions::Shrink, JS::GCReason::API);
+	JS_SetGCParameter(m_cx, JSGC_INCREMENTAL_GC_ENABLED, true);
+	JS_SetGCParameter(m_cx, JSGC_PER_ZONE_GC_ENABLED, false);
 }
 
 void ScriptContext::PrepareZonesForIncrementalGC() const
 {
 	for (JS::Realm* const& realm : m_Realms)
-		JS::PrepareZoneForGC(js::GetRealmZone(realm));
+		JS::PrepareZoneForGC(m_cx, js::GetRealmZone(realm));
 }
Index: source/scriptinterface/ScriptConversions.cpp
===================================================================
--- source/scriptinterface/ScriptConversions.cpp
+++ source/scriptinterface/ScriptConversions.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -105,7 +105,7 @@
 	if (!str)
 		FAIL("Argument must be convertible to a string");
 
-	if (JS_StringHasLatin1Chars(str))
+	if (JS::StringHasLatin1Chars(str))
 	{
 		size_t length;
 		JS::AutoCheckCannotGC nogc;
Index: source/scriptinterface/ScriptExtraHeaders.h
===================================================================
--- source/scriptinterface/ScriptExtraHeaders.h
+++ source/scriptinterface/ScriptExtraHeaders.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -60,6 +60,10 @@
 #include "js/Proxy.h"
 #include "js/Warnings.h"
 
+#include "js/experimental/TypedData.h"
+
+#include "js/friend/ErrorMessages.h"
+
 #undef signbit
 
 #if MSC_VERSION
Index: source/scriptinterface/ScriptInterface.cpp
===================================================================
--- source/scriptinterface/ScriptInterface.cpp
+++ source/scriptinterface/ScriptInterface.cpp
@@ -533,11 +533,11 @@
 		return false;
 	if (found)
 	{
-		JS::Rooted<JS::PropertyDescriptor> desc(rq.cx);
-		if (!JS_GetOwnPropertyDescriptor(rq.cx, global, name, &desc))
+		JS::Rooted<mozilla::Maybe<JS::PropertyDescriptor>> desc(rq.cx);
+		if (!JS_GetOwnPropertyDescriptor(rq.cx, global, name, &desc) || !desc.isSome())
 			return false;
 
-		if (!desc.writable())
+		if (!desc->writable())
 		{
 			if (!replace)
 			{
@@ -547,7 +547,7 @@
 
 			// This is not supposed to happen, unless the user has called SetProperty with constant = true on the global object
 			// instead of using SetGlobal.
-			if (!desc.configurable())
+			if (!desc->configurable())
 			{
 				ScriptException::Raise(rq, "The global \"%s\" is permanent and cannot be hotloaded", name);
 				return false;
Index: source/scriptinterface/ScriptTypes.h
===================================================================
--- source/scriptinterface/ScriptTypes.h
+++ source/scriptinterface/ScriptTypes.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2020 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -73,7 +73,7 @@
 # pragma GCC diagnostic pop
 #endif
 
-#if MOZJS_MAJOR_VERSION != 78
+#if MOZJS_MAJOR_VERSION != 91
 #error Your compiler is trying to use an incorrect major version of the \
 SpiderMonkey library. The only version that works is the one in the \
 libraries/spidermonkey/ directory, and it will not work with a typical \
@@ -81,7 +81,7 @@
 include paths.
 #endif
 
-#if MOZJS_MINOR_VERSION != 6
+#if MOZJS_MINOR_VERSION != 13
 #error Your compiler is trying to use an untested minor version of the \
 SpiderMonkey library. If you are a package maintainer, please make sure \
 to check very carefully that this version does not change the behaviour \
Index: source/simulation2/scripting/EngineScriptConversions.cpp
===================================================================
--- source/simulation2/scripting/EngineScriptConversions.cpp
+++ source/simulation2/scripting/EngineScriptConversions.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -62,7 +62,7 @@
 		return;
 	}
 
-	JS_SetPrivate(obj, static_cast<void*>(val));
+	JS::SetPrivate(obj, static_cast<void*>(val));
 	ret.setObject(*obj);
 }
 
Index: source/simulation2/serialization/BinarySerializer.cpp
===================================================================
--- source/simulation2/serialization/BinarySerializer.cpp
+++ source/simulation2/serialization/BinarySerializer.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2022 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -219,9 +219,9 @@
 		else
 		{
 			// Find type of object
-			const JSClass* jsclass = JS_GetClass(obj);
+			const JSClass* jsclass = JS::GetClass(obj);
 			if (!jsclass)
-				throw PSERROR_Serialize_ScriptError("JS_GetClass failed");
+				throw PSERROR_Serialize_ScriptError("JS::GetClass failed");
 
 			JSProtoKey protokey = JSCLASS_CACHED_PROTO_KEY(jsclass);
 
@@ -321,10 +321,11 @@
 			JS::RootedValue propval(rq.cx);
 
 			// Forbid getters, which might delete values and mess things up.
-			JS::Rooted<JS::PropertyDescriptor> desc(rq.cx);
-			if (!JS_GetPropertyDescriptorById(rq.cx, obj, id, &desc))
+			JS::Rooted<mozilla::Maybe<JS::PropertyDescriptor>> desc(rq.cx);
+			JS::RootedObject holder(rq.cx);
+			if (!JS_GetPropertyDescriptorById(rq.cx, obj, id, &desc, &holder))
 				throw PSERROR_Serialize_ScriptError("JS_GetPropertyDescriptorById failed");
-			if (desc.hasGetterObject())
+			if (desc.isSome() && desc->hasGetter())
 				throw PSERROR_Serialize_ScriptError("Cannot serialize property getters");
 
 			// Get the property name as a string
@@ -354,7 +355,7 @@
 			JS::RootedString string(rq.cx, JS_GetFunctionId(func));
 			if (string)
 			{
-				if (JS_StringHasLatin1Chars(string))
+				if (JS::StringHasLatin1Chars(string))
 				{
 					size_t length;
 					JS::AutoCheckCannotGC nogc;
@@ -440,7 +441,7 @@
 	size_t length;
 	JS::AutoCheckCannotGC nogc;
 	// Serialize strings directly as UTF-16 or Latin1, to avoid expensive encoding conversions
-	bool isLatin1 = JS_StringHasLatin1Chars(string);
+	bool isLatin1 = JS::StringHasLatin1Chars(string);
 	m_Serializer.Bool("isLatin1", isLatin1);
 	if (isLatin1)
 	{