Fixing Firefox 43's Failed h.264 Enablement on Linux

I tried enabling full hardware acceleration for YouTube on Linux a while back in this post. If you unfortunately did the same, upgrading to Firefox 43 today probably broke YouTube video loading for you.

First it’s this…

Then it’s this…

After digging around for a while I finally found the fix…

The cause is simple enough — again, spotted on the Archlinux forums:

Make sure media.fragmented-mp4.gmp.enable is false.

Restart Firefox and you can go back to watching videos via HTML5.