Edit-2 2020/09/14
i figured out some problem when watching live stream. rotation button will be broken after you clicked it.
please update to v5.0.3 maybe this fix your problem as well

Edit 2020/09/14
feel free to reply me if you figured out the problems. thanks

Edit 2020/09/13
i still didn't find any issue both mac / windows on this browser version (80.0.1) . could you try to remove and reinstall the new version add-on (v.5.0.2 update today) ?
after installation, try reloading the Youtube page.

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Hi. I have tried many videos but I haven't found any issues.
Which version of Firefox are you using ?
Not working with old or new layout ?
Can you share a link where the button doesn't work?