Created attachment 549434 [details] output of emerge --info Similar to bug #614360, I get a "libavcodec may be vulnerable or is not supported, and should be updated to play video." on multiple websites. The same reproducer from that bug also exhibits the error: http://i.imgur.com/GRARvMG.gifv
Created attachment 549436 [details] equery uses firefox
Created attachment 549438 [details] equery uses libav
There's nothing wrong with that message -- it is correct: libav in Gentoo is outdated and has known vulnerabilities and Firefox knows about that. Not a bug within www-client/firefox.
I bumped libav this weekend. Can you please tell us if the warning is gone with =media-video/libav-12.3?