Yes, thanks to the open source H.264 codec from Cisco. This is about open source...

astrange · on Sept 9, 2015

The way that article is written makes it sound like a closed-source codec, but it is actually open:

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.

marquis · on Sept 9, 2015

It's about the patents.

"while OpenH264 is not truly open, at least it is the most open widely used video codec"

http://andreasgal.com/2014/10/14/openh264-now-in-firefox/

callesgg · on Sept 10, 2015

Well Web rtc in firefox uses the "H.264 codec from Cisco".

Normal videos like youtube uses the operating system decoder.