firefox: enable necko wifi scanner

Tied to the geolocation support flag. On Linux this uses the DBus
interface of NetworkManager to query visible accesspoints and relay them
to Mozilla location service in return for position approximation.

pkgs/applications/networking/browsers/firefox/common.nix

@@ -262,7 +262,6 @@ buildStdenv.mkDerivation ({
     "--enable-system-pixman"
     #"--enable-system-cairo"
     "--disable-tests"
-    "--disable-necko-wifi" # maybe we want to enable this at some point
     "--disable-updater"
     "--enable-default-toolkit=${default-toolkit}"
     "--with-libclang-path=${llvmPackages.libclang.lib}/lib"
@@ -286,6 +285,7 @@ buildStdenv.mkDerivation ({
   ++ flag pulseaudioSupport "pulseaudio"
   ++ flag ffmpegSupport "ffmpeg"
   ++ flag jemallocSupport "jemalloc"
+  ++ flag geolocationSupport "necko-wifi"
   ++ flag gssSupport "negotiateauth"
   ++ flag webrtcSupport "webrtc"
   ++ flag crashreporterSupport "crashreporter"