Any relevant-looking messages in the Web Console ?

• https://developer.mozilla.org/en-US/docs/Tools/Web_Console

Can you provide screenshots and links to the pages giving you issues?

Here are three screenshots two of the sites and one of the Console.

Make sure you have the latest FFmpeg and libavcodec packages installed.

5.0.1 of ffmpg. How do I check libavcodec?

ffmpeg -version and see screenshot. Did you ever try Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf

Can you provide links to the sites with the issue?

What OS? What desktop? X11 or Wayland?

Operating System: openSUSE Tumbleweed 20220904 KDE Plasma Version: 5.25.4 KDE Frameworks Version: 5.97.0 Qt Version: 5.15.5 Kernel Version: 5.19.2-1-default (64-bit) Graphics Platform: X11 Processors: 4 × Intel® Core™ i7-4810MQ CPU @ 2.80GHz Memory: 31.0 GiB of RAM Graphics Processor: Quadro K3100M/PCIe/SSE2 Product Name: HP ZBook 17 G2

As stated Fedora 36 using Wayland , Firefox 104.0.1. The problem still exists opening Firefox in Safe Mode. (troubleshoot mode)

I have tried the Gnome WEB browser and have the same problem. So it seems it is not Firefox specific?

I did a "sudo dnf remove libswscale-free libavcodec-free" and now video is working in Firefox. I am not sure why this worked. Maybe someone can explain why? However video is still not working in Gnome WEB browser. Is there a forum for Gnome applications?

Good work. Mark it as resolved.

Solved for Firefox but not Gnome WEB browser.