Yes, thanks to the open source H.264 codec from Cisco. This is about open source options and I think Firefox's decisions are completely valid.
https://gigaom.com/2014/10/14/h-264-support-arrives-in-firef...
https://gigaom.com/2014/10/14/h-264-support-arrives-in-firef...
https://github.com/cisco/openh264
and the code is better than I expected from a commercial project, it even uses may_alias properly. I wonder why the decoder doesn't support CPU multithreading, though? Slice threads are pretty simple to add.
"while OpenH264 is not truly open, at least it is the most open widely used video codec"
Normal videos like youtube uses the operating system decoder.