Site works in Troubleshoot mode, but not in regular mode FF

[Vojer]

https://heldenvanhetverzet.be/voorleesmarathon does not show the streaming video in regular mode.
Once you switch on Troubleshoot mode, the streaming video works as expected

[siffemcon]

Works for me. Does that also happen in Troubleshoot mode (https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode)?

[siffemcon]

Did you edit your post after you saw my comment, or did just miss it? Anyway,

go back to normal mode > disable all your add-ons > re-enable one at a time and test.

If you have a lot of add-ons, disable half of them. If the problem still exists, re-enable them, disable the other half, and narrow it down in a similar fashion.

[Vojer]

a private session works fine.