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
  +, yasm, mesa
   
   , # If you want the resulting program to call itself "Firefox" instead
     # of "Shiretoko" or whatever, enable this option.  However, those
  
positive.code: 
  rec {
  
    firefoxVersion = "4.0";
    
    xulVersion = "2.0"; # this attribute is used by other packages
  
    
    src = fetchurl {
      url = "http://releases.mozilla.org/pub/mozilla.org/firefox/releases/${firefoxVersion}/source/firefox-${firefoxVersion}.source.tar.bz2";
      sha1 = "403da9dd65662e5c4dd34299214e04cb6f80575e";
    };
  
    
  
negative.code:     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];
  