I was receiving the error “We cannot play the video in this browser. Please try a different web browser.” I noticed they worked in Chrome but not Firefox; in my experience this is because Firefox has some additional protections against non-free software that CHrome doesn’t care about. I identified that my browser was missing some codecs checking youtube and spotting the red-boxes under “what does this browser support?”

Looking around I found this solution.

My system: OpenSUSE Tumbleweed

Install the Pacman [Extras] Repos

I did:

sudo zypper ar -cfp 90 https://ftp.gwdg.de/pub/linux/misc/packman/suse/openSUSE_Tumbleweed/ packman

Install LibAV codecs

It recommended installing all libav stuff, so I did this:

sudo zypper in libav*

Switch to using the pacman repos instead of Tumbleweed ones

sudo zypper dup --from packman --allow-vendor-change

Conclusion

Now I restarted my Firefox entirely and heading back to Youtube, all boxes are blue. Twitter gifs/videos now work.