anchor.diff:  { 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
  -, libvpx, yasm, mesa, wirelesstools
  +, libvpx, yasm, mesa
   
   , # If you want the resulting program to call itself "Firefox" instead
     # of "Shiretoko" or whatever, enable this option.  However, those
  
positive.code:     buildInputs =
        [ pkgconfig gtk perl zip libIDL libjpeg zlib cairo bzip2 python
          dbus dbus_glib pango freetype fontconfig alsaLib nspr libnotify
          xlibs.pixman libvpx yasm mesa wirelesstools
        ];
  
      propagatedBuildInputs = [xulrunner];
  
negative.code: 
      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";
  
  