anchor.diff:        "--with-system-nspr"
         "--with-system-nss"
         "--with-system-libevent"
  -      "--with-system-libvpx"
  +      #"--with-system-libvpx" # needs 1.5.0
         "--with-system-png" # needs APNG support
         "--with-system-icu"
         "--enable-system-ffi"
  
positive.code: 
    firefox-unwrapped = common {
      pname = "firefox";
      version = "45.0.2";
      sha512 = "8c0b7afb41a1a405fe499299d1a8b1138dac52b9ad67bfc8761b70a26f330581c2aa1d76d67075896ec3a0c3f5367b8b58365ebc8b3a01f801fa37071b3de526";
    };
  
    firefox-esr-unwrapped = common {
  
negative.code:       alsaLib nspr nss libnotify xorg.pixman yasm mesa
        xorg.libXScrnSaver xorg.scrnsaverproto pysqlite
        xorg.libXext xorg.xextproto sqlite unzip makeWrapper
        hunspell libevent libstartup_notification /* libvpx */ /* cairo */
        gstreamer gst_plugins_base icu libpng jemalloc
        libpulseaudio # only headers are needed
      ]
  