The Troubleshooting Information page (about:support) should list the available gstreamer version for systems that support it. (like it already does for the mesa version) The gstreamer support is still a bit buggy for some people, so this version will be needed for Linux and Mac users in order to get support and file bugs. If there's any other media-related package used directly or indirectly, it would be nice if their versions could be listed too.

I agree, this sounds like a very good idea.

gstreamer is going in bug 1234092