Main reason why Firefox performs so horrendously bad with H.264 encoded HTML5 video services (Youtube etc) is the integration of Cisco’s OpenH264. Sure it’s free, but apparently it’s also worth as much as it costs. It apparently lacks any kind of hardware acceleration and makes my AMD E-450 APU laptop literally scream and sweat in pain when it tries to play Youtube videos, because it tries to decode everything on weak CPU. The GPU part was just doing nothing and it has a DirectX 11 grade core within the APU. It’s so bad it makes 1080p30 or 720p60 entirely unplayable. Mozilla first bundled this codec with Firefox 33, but I’ve only noticed it when they hit Firefox 37. It’s when Youtube also switched to full HTML5 mode. And that’s when shit started…
I just don’t get it why is it used as primary decoder and not as a fallback if nothing else is found. Stupid logic from Mozilla…
Disable this dumb software OpenH264 decoder so that something native from Windows kicks in instead. In my case AMD Video Decoder (most likely), providing me with a proper hardware accelerated decoder which is more efficient and also super fast since it’s using GPU instead of slow CPU.
How to disable integrated Firefox OpenH264 software decoder?
Type about:config into the Firefox URL bar and hit ENTER.
In the Search field above, enter (just copy & paste it there):
Double click the found entry and it’ll switch itself to FALSE (which means disabled OpenH264 decoder).
Restart the Firefox and try Youtube again. It should play super smoothly now…
Special thanks to JayhawksRock from Mozillazine forums for telling me this secret.