In the beginning I had to configure a plugin to get any video from sources like Youtube playing. I’ve done that and it works for about 2/3rds of the videos. But some still don’t work, and I don’t get more infos or warnings or error messages for it. I likely didn’t do more than install the plugin recommended by firefox after the initial installation.
I am doing some modifications to the loading pages though, since I’m using uBlock origin to block ads. Could this block the whole video from playing? I haven’t seen that happen in other systems, though (not Fedora, but including RHEL desktop, Windows, OSX, Ubuntu). So it would surprise me if that is it.
This is still an issue with Fedora 36. Content sites offer videos in various formats as a fallback, so it’s hard to tell what video format is/isn’t working on a particular page. You can open the Firefox developer tools and look in its Console tab for warnings like
The video on this page can’t be played. Your system may not have
the required video codecs for:
video/mp4; codecs="avc1.4D401E", video/mp4;
I find this video page helpful because it has a sample of each video format without fallback. In my case, WebM video works in Firefox, but MPEG, which I think is .mp4 “H264” video, doesn’t. YouTube offers videos in WebM, but Twitter and Facebook seem to prefer mp4. What’s confusing is Firefox has an H264 video plug-in from Cisco that you can install and activate (here’s Fedora’s guide); but it seems to only enable WebRTC video calls, not video playback.
So, you need to install non-free video codecs. Fedora’s guide Installing plugins for playing movies and musicseems to be the right instructions. What’s confusing is that guide suggests installing gstreamer plug-ins, but Firefox can also/instead use the multimedia libraries from FFmpeg to play video, and I think this is the default in the Fedora Firefox package (in about:config, media.ffmpeg.enabled defaults to true).
So I think you need to enable the RPM Fusion packages and then install ffmpeg-libs (in a terminal, sudo dnf install ffmpeg-libs), then restart Firefox. That worked for me, and I didn’t install gstreamer plugins, lame, or the Multimedia group as the Fedora docs suggest. Your mileage may vary. (Some guides on the web tell you to install the FFmpeg video player, which works because that installs the ffmpeg-libs as well; but I already have installed VLC to play media.)
If this works for others, please @erikbask somehow unvote your solution and vote this one.