anchor.diff:      inherit src;
   
       buildInputs =
  -      [ pkgconfig gtk perl zip libIDL libjpeg libpng zlib cairo bzip2
  +      [ pkgconfig gtk perl zip libIDL libjpeg libpng zlib 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 pysqlite
           xlibs.libXext xlibs.xextproto sqlite unzip makeWrapper
           hunspell libevent libstartup_notification libvpx
  -      ];
  +      ] ++ optional useSystemCairo cairo;
   
       configureFlags =
         [ "--enable-application=xulrunner"
  
positive.code: 
      enableParallelBuilding = true;
  
      patches = [
        ./system-cairo.patch # accepted upstream, probably in 22
      ];
  
      preConfigure =
        ''
  
negative.code:       "--with-system-libvpx"
        # "--with-system-png" # <-- "--with-system-png won't work because the system's libpng doesn't have APNG support"
        "--enable-startup-notification"
        "--enable-system-ffi"
        "--enable-system-hunspell"
        "--enable-system-pixman"
        "--enable-system-sqlite"
        "--disable-crashreporter"
        "--disable-tests"
        "--disable-necko-wifi" # maybe we want to enable this at some point
        "--disable-installer"
        "--disable-updater"
      ] ++ optional useSystemCairo "--enable-system-cairo";
  
  
    xulrunner = stdenv.mkDerivation rec {
  