diff --git a/pkgs/applications/networking/browsers/firefox/5.0.nix b/pkgs/applications/networking/browsers/firefox/5.0.nix
new file mode 100644
index 000000000000..8848219845ef
--- /dev/null
+++ b/pkgs/applications/networking/browsers/firefox/5.0.nix
@@ -0,0 +1,170 @@
+{ stdenv, fetchurl, pkgconfig, gtk, pango, perl, python, zip, libIDL
+, libjpeg, libpng, zlib, cairo, dbus, dbus_glib, bzip2, xlibs
+, freetype, fontconfig, file, alsaLib, nspr, nss, libnotify
+, yasm, mesa
+
+, # If you want the resulting program to call itself "Firefox" instead
+  # of "Shiretoko" or whatever, enable this option.  However, those
+  # binaries may not be distributed without permission from the
+  # Mozilla Foundation, see
+  # http://www.mozilla.org/foundation/trademarks/.
+  enableOfficialBranding ? false
+}:
+
+assert stdenv.gcc ? libc && stdenv.gcc.libc != null;
+
+rec {
+
+  firefoxVersion = "5.0";
+  
+  xulVersion = "5.0"; # this attribute is used by other packages
+
+  versionSuffix = "-rc1";
+
+  
+  src = fetchurl {
+    url = "http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/5.0-candidates/build1/source/firefox-${firefoxVersion}.source.tar.bz2";
+    sha256 = "0i6zxvhvf717bzz3mwlbvrk601k81r38fym0fv2nlvr9r207vybb";
+  };
+
+  
+  commonConfigureFlags =
+    [ "--enable-optimize"
+      "--disable-debug"
+      "--enable-strip"
+      "--with-system-jpeg"
+      "--with-system-zlib"
+      "--with-system-bz2"
+      "--with-system-nspr"
+      # "--with-system-nss"
+      # "--with-system-png" # <-- "--with-system-png won't work because the system's libpng doesn't have APNG support"
+      # Disabled system Cairo for now because it causes gradients in tabs etc. to be missing.
+      # "--enable-system-cairo"
+      # Compiling with the Nixpkgs SQLite gives:
+      # "configure: error: System SQLite library is not compiled with SQLITE_SECURE_DELETE."
+      # "--enable-system-sqlite"
+      "--disable-crashreporter"
+      "--disable-tests"
+      "--disable-necko-wifi" # maybe we want to enable this at some point
+      "--disable-installer" 
+      "--disable-updater"
+    ];
+
+
+  xulrunner = stdenv.mkDerivation rec {
+    name = "xulrunner-${xulVersion}${versionSuffix}";
+    
+    inherit src;
+
+    buildInputs =
+      [ pkgconfig gtk perl zip libIDL libjpeg libpng zlib cairo bzip2
+        python dbus dbus_glib pango freetype fontconfig xlibs.libXi
+        xlibs.libX11 xlibs.libXrender xlibs.libXft xlibs.libXt file
+        alsaLib nspr /* nss */ libnotify xlibs.pixman yasm mesa
+	xlibs.libXScrnSaver xlibs.scrnsaverproto
+	xlibs.libXext xlibs.xextproto
+      ];
+
+    configureFlags =
+      [ "--enable-application=xulrunner"
+        "--disable-javaxpcom"
+      ] ++ commonConfigureFlags;
+
+    enableParallelBuilding = true;
+      
+    # Hack to work around make's idea of -lbz2 dependency
+    preConfigure =
+      ''
+        find . -name Makefile.in -execdir sed -i '{}' -e '1ivpath %.so ${
+          stdenv.lib.concatStringsSep ":" 
+            (map (s : s + "/lib") (buildInputs ++ [stdenv.gcc.libc]))
+        }' ';'
+      '';
+
+    # !!! Temporary hack.
+    preBuild =
+      ''
+        export NIX_ENFORCE_PURITY=
+      '';
+
+    installFlags = "SKIP_GRE_REGISTRATION=1";
+
+    postInstall = ''
+      # Fix some references to /bin paths in the Xulrunner shell script.
+      substituteInPlace $out/bin/xulrunner \
+          --replace /bin/pwd "$(type -tP pwd)" \
+          --replace /bin/ls "$(type -tP ls)"
+
+      # Fix run-mozilla.sh search
+      libDir=$(cd $out/lib && ls -d xulrunner-[0-9]*)
+      echo libDir: $libDir
+      test -n "$libDir"
+      cd $out/bin
+      mv xulrunner ../lib/$libDir/
+
+      for i in $out/lib/$libDir/*; do 
+          file $i;
+          if file $i | grep executable &>/dev/null; then 
+              ln -s $i $out/bin
+          fi;
+      done;
+      rm -f $out/bin/run-mozilla.sh
+    ''; # */
+
+    meta = {
+      description = "Mozilla Firefox XUL runner";
+      homepage = http://www.mozilla.com/en-US/firefox/;
+    };
+
+    passthru = { inherit gtk; version = xulVersion; };
+  };
+
+
+  firefox = stdenv.mkDerivation rec {
+    name = "firefox-${firefoxVersion}${versionSuffix}";
+
+    inherit src;
+
+    enableParallelBuilding = true;
+      
+    buildInputs =
+      [ pkgconfig gtk perl zip libIDL libjpeg zlib cairo bzip2 python
+        dbus dbus_glib pango freetype fontconfig alsaLib nspr libnotify
+        xlibs.pixman yasm mesa
+      ];
+
+    propagatedBuildInputs = [xulrunner];
+
+    configureFlags =
+      [ "--enable-application=browser"
+        "--with-libxul-sdk=${xulrunner}/lib/xulrunner-devel-${xulrunner.version}"
+        "--enable-chrome-format=jar"
+      ]
+      ++ commonConfigureFlags
+      ++ stdenv.lib.optional enableOfficialBranding "--enable-official-branding";
+
+    # Hack to work around make's idea of -lbz2 dependency
+    preConfigure =
+      ''
+        find . -name Makefile.in -execdir sed -i '{}' -e '1ivpath %.so ${
+          stdenv.lib.concatStringsSep ":" 
+            (map (s : s + "/lib") (buildInputs ++ [stdenv.gcc.libc]))
+        }' ';'
+      '';
+
+    postInstall =
+      ''
+        ln -s ${xulrunner}/lib/xulrunner-${xulrunner.version} $(echo $out/lib/firefox-*)/xulrunner
+      ''; # */
+
+    meta = {
+      description = "Mozilla Firefox - the browser, reloaded";
+      homepage = http://www.mozilla.com/en-US/firefox/;
+    };
+
+    passthru = {
+      inherit gtk xulrunner nspr;
+      isFirefox3Like = true;
+    };
+  };
+}
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 28f706e642cc..3315184f6422 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -6225,6 +6225,13 @@ let
 
   firefox40Wrapper = wrapFirefox firefox40Pkgs.firefox "firefox" "";
 
+  firefox50Pkgs = callPackage ../applications/networking/browsers/firefox/5.0.nix {
+    inherit (gtkLibs) gtk pango;
+    inherit (gnome) libIDL;
+  };
+
+  firefox50Wrapper = wrapFirefox firefox50Pkgs.firefox "firefox" "";
+
   flac = callPackage ../applications/audio/flac { };
 
   flashplayer = flashplayer10;