Comment # 1 on bug 1199210 from Wolfgang Rosenauer

For me everything still works as always with TW and FF100.

The difference might be that I still have the packman libavcodec installed
which supports everything.

I heard that some people of openSUSE/SUSE worked on getting H.264 support
through openh264 but nobody ever talked to me as Firefox maintainer if there is
anything I need to take care of.

I currently have
libavcodec58_134-4.4.1-10.6.x86_64
libavcodec57-3.4.9-1.28.x86_64
from Packman's Essentials installed and it's working fine.

What is installed for you?
ls -l /usr/lib64/libavcodec*