firefoxPackages: add `extraConfigureFlags` to common builder, move `--disable-loop` flag to tor-browser expression

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

@@ -1,5 +1,5 @@
 { pname, version, updateScript ? null
-, src, patches ? [], overrides ? {}, meta
+, src, patches ? [], extraConfigureFlags ? [], overrides ? {}, meta
 , isTorBrowserLike ? false }:
 
 { lib, stdenv, pkgconfig, pango, perl, python, zip, libIDL
@@ -29,7 +29,6 @@
 # Set to `privacySupport` or `false`.
 
 , webrtcSupport ? !privacySupport
-, loopSupport ? !privacySupport || !isTorBrowserLike
 , geolocationSupport ? !privacySupport
 , googleAPISupport ? geolocationSupport
 , crashreporterSupport ? false
@@ -48,7 +47,6 @@
 }:
 
 assert stdenv.cc ? libc && stdenv.cc.libc != null;
-assert !isTorBrowserLike -> loopSupport; # can't be disabled on firefox :(
 
 let
   flag = tf: x: [(if tf then "--enable-${x}" else "--disable-${x}")];
@@ -147,8 +145,6 @@ stdenv.mkDerivation (rec {
   ++ flag ffmpegSupport "ffmpeg"
   ++ lib.optional (!ffmpegSupport) "--disable-gstreamer"
   ++ flag webrtcSupport "webrtc"
-  ++ lib.optionals isTorBrowserLike
-       (flag loopSupport "loop")
   ++ flag geolocationSupport "mozril-geoloc"
   ++ lib.optional googleAPISupport "--with-google-api-keyfile=ga"
   ++ flag crashreporterSupport "crashreporter"
@@ -159,7 +155,8 @@ stdenv.mkDerivation (rec {
                     else [ "--disable-debug" "--enable-release"
                            "--enable-optimize"
                            "--enable-strip" ])
-  ++ lib.optional enableOfficialBranding "--enable-official-branding";
+  ++ lib.optional enableOfficialBranding "--enable-official-branding"
+  ++ extraConfigureFlags;
 
   enableParallelBuilding = true;
 

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

@@ -49,6 +49,7 @@ rec {
     pname = "tor-browser";
     version = "6.5.2";
     isTorBrowserLike = true;
+    extraConfigureFlags = [ "--disable-loop" ];
 
     # FIXME: fetchFromGitHub is not ideal, unpacked source is >900Mb
     src = fetchFromGitHub {