If THEOplayer is not working in Firefox, there could be several reasons for this issue. Here are some troubleshooting steps you can try to resolve the problem:

Clear Browser Cache: Cached data may sometimes cause conflicts with the player. Clear your browser cache and try again.

Update Firefox: Make sure you are using the latest version of Firefox. Outdated browsers may have compatibility issues with certain applications.

Disable Browser Extensions: Some browser extensions or add-ons may interfere with THEOplayer's functionality. Try disabling any extensions and see if the player works.

It works for me. Does it still happen in Troubleshoot Mode?

You are right, thanks, it works in "Troubleshoot mode" (Now I need to figure out which useful extension to deactivate, or just swich to Chrome for such video sites, or that Firefox solves it).

Had no issue playing the link. And I use standard Firefox setup and minimal Addons. Firefox can't be faulted for Addon issues that is to contact the Addon developer if their Addon is the issue.