anchor.diff:        "--with-system-libevent"
         "--with-system-libvpx"
         "--with-system-png"
  -      "--with-system-icu"
  +      # "--with-system-icu" # causes ‘ar: invalid option -- 'L'’ in Firefox 28.0
         "--enable-system-ffi"
         "--enable-system-hunspell"
         "--enable-system-pixman"
  
positive.code: 
  rec {
  
    firefoxVersion = "27.0.1";
  
    xulVersion = "27.0.1"; # this attribute is used by other packages
  
  
    src = fetchurl {
      urls = [
          # It is better to use this url for official releases, to take load off Mozilla's ftp server.
          "http://releases.mozilla.org/pub/mozilla.org/firefox/releases/${firefoxVersion}/source/firefox-${firefoxVersion}.source.tar.bz2"
          # Fall back to this url for versions not available at releases.mozilla.org.
          "http://ftp.mozilla.org/pub/mozilla.org/firefox/releases/${firefoxVersion}/source/firefox-${firefoxVersion}.source.tar.bz2"
      ];
      sha256 = "13qd53yf8dn9m03p4x5ml9h3mys60nba5nz82lcvaq7ycp1pl1bn";
    };
  
    commonConfigureFlags =
  
negative.code:       "--disable-necko-wifi" # maybe we want to enable this at some point
        "--disable-installer"
        "--disable-updater"
        "--disable-pulseaudio"
      ] ++ (if debugBuild then [ "--enable-debug" "--enable-profiling"]
                          else [ "--disable-debug" "--enable-release"
                                 "--enable-optimize" "--enable-strip" ]);
  