diff --git a/pkgs/development/interpreters/spidermonkey/78.nix b/pkgs/development/interpreters/spidermonkey/78.nix
new file mode 100644
index 000000000000..84897ee84639
--- /dev/null
+++ b/pkgs/development/interpreters/spidermonkey/78.nix
@@ -0,0 +1,118 @@
+{ stdenv
+, fetchurl
+, fetchpatch
+, autoconf213
+, pkgconfig
+, perl
+, python3
+, zip
+, buildPackages
+, which
+, readline
+, zlib
+, icu67
+, cargo
+, rustc
+, rust-cbindgen
+, yasm
+, llvmPackages
+, nspr
+}:
+
+stdenv.mkDerivation rec {
+  pname = "spidermonkey";
+  version = "78.1.0";
+
+  src = fetchurl {
+    url = "mirror://mozilla/firefox/releases/${version}esr/source/firefox-${version}esr.source.tar.xz";
+    sha256 = "18k47dl9hbnpqw69csxjar5dhwa7r8k7j9kvcfgmwb1iv6ba601n";
+  };
+
+  outputs = [ "out" "dev" ];
+  setOutputFlags = false; # Configure script only understands --includedir
+
+  nativeBuildInputs = [
+    autoconf213
+    cargo
+    llvmPackages.llvm # for llvm-objdump
+    perl
+    pkgconfig
+    python3
+    rust-cbindgen
+    rustc
+    which
+    yasm # to buid icu? seems weird
+    zip
+  ];
+
+  buildInputs = [
+    icu67
+    nspr
+    readline
+    zlib
+  ];
+
+  patches = [
+    # https://mail.gnome.org/archives/distributor-list/2020-August/msg00000.html
+    (fetchpatch {
+      url = "https://github.com/ptomato/mozjs/commit/b2974f8a6558d2dc4517b49ee313a9900a853285.patch";
+      sha256 = "1bl5mbx7gmad6fmpc427263i1ychi2linpg69kxlr2w91r5m6ji3";
+    })
+    (fetchpatch {
+      url = "https://github.com/ptomato/mozjs/commit/e5a2eb99f653ae03c67e536df1d55d265a0a1605.patch";
+      sha256 = "0xhy63nw2byibmjc41yh6dwpg282nylganrs5aprn9pbqbcpsvif";
+    })
+  ];
+
+  preConfigure = ''
+    export CXXFLAGS="-fpermissive"
+    export LIBXUL_DIST=$out
+    export PYTHON="${buildPackages.python3.interpreter}"
+
+    # We can't build in js/src/, so create a build dir
+    mkdir obj
+    cd obj/
+    configureScript=../js/src/configure
+  '';
+
+  configureFlags = [
+    "--with-system-zlib"
+    "--with-system-nspr"
+    "--with-system-icu"
+    "--with-intl-api"
+    "--enable-readline"
+    "--enable-shared-js"
+    "--disable-jemalloc"
+    # Fedora and Arch disable optimize, but it doesn't seme to be necessary
+    # It turns on -O3 which some gcc version had a problem with:
+    # https://src.fedoraproject.org/rpms/mozjs38/c/761399aba092bcb1299bb4fccfd60f370ab4216e
+    "--enable-optimize"
+    "--enable-release"
+  ] ++ stdenv.lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    # Spidermonkey seems to use different host/build terminology for cross
+    # compilation here.
+    "--host=${stdenv.buildPlatform.config}"
+    "--target=${stdenv.hostPlatform.config}"
+  ];
+
+  configurePlatforms = [ ];
+
+  depsBuildBuild = [ buildPackages.stdenv.cc ];
+
+  # Remove unnecessary static lib
+  preFixup = ''
+    moveToOutput bin/js60-config "$dev"
+    rm $out/lib/libjs_static.ajs
+    ln -s $out/bin/js60 $out/bin/js
+  '';
+
+  enableParallelBuilding = true;
+
+  meta = with stdenv.lib; {
+    description = "Mozilla's JavaScript engine written in C/C++";
+    homepage = "https://developer.mozilla.org/en/SpiderMonkey";
+    license = licenses.gpl2; # TODO: MPL/GPL/LGPL tri-license.
+    maintainers = [ maintainers.abbradar ];
+    platforms = platforms.linux;
+  };
+}
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 20090f0f299a..ddf2b1495fd8 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -10391,6 +10391,7 @@ in
   }));
   spidermonkey_60 = callPackage ../development/interpreters/spidermonkey/60.nix { };
   spidermonkey_68 = callPackage ../development/interpreters/spidermonkey/68.nix { };
+  spidermonkey_78 = callPackage ../development/interpreters/spidermonkey/78.nix { };
   spidermonkey = spidermonkey_38;
 
   ssm-agent = callPackage ../applications/networking/cluster/ssm-agent { };