Hey Ananda, could you add a screenshot? And does the same thing happen also in the stable version of Firefox or only Beta?

heres is a screenshot. i only use beta, system has been setup this week due too a new pc, i copied a ff recent made backup to ff profile, video behaves nornal for one day and now ...as you can see in the screenshot

Interesting, I am on stable and can't reproduce, but before I file a bug for this, let's make sure this is not due to a preference you have on your Firefox. Please do the following and let me know if anything worked: <!-- CONTRIBUTOR NOTE: 1. Check whether the question contains an exact URL / site name. If not, ask for it. 2. If you can, try to reproduce the issue in a browser different from Firefox. If it also reproduces itself there, then it's not a Firefox issue. Explain it to the OP. If it doesn't, proceed to step 3. 3. If you can, try to reproduce the issue in a CLEAN PROFILE. If it's reproducible, please report it yourself on WebCompat (https://webcompat.com/issues/new), preferably with your GitHub account, or directly on Bugzilla (https://bugzilla.mozilla.org/enter_bug.cgi?product=Web+Compatibility&component=Site+Reports). 4. If the issue doesn't reproduce itself, or you can't try that (e.g., when an account on the problematic website is needed), proceed to the steps below. --> # Please check if you have [[Enhanced Tracking Protection in Firefox for desktop|Enhanced Tracking Protection]] (ETP) enabled. You can do that by clicking the shield [[Image:Fx89ShieldIcon]] icon in the left part of the address bar. #* If ETP is enabled, try disabling it. # If the problem is not fixed, try [[How to clear the Firefox cache|clearing Firefox cache]]. # If it does not help, try [[Clear cookies and site data in Firefox|clearing cookies and data]] for the website you experience troubles with (''warning: you will be logged out on this website''). # If it also does not help, try [[Diagnose Firefox issues using Troubleshoot Mode|running Firefox in Troubleshoot Mode]]. If the problem doesn't persist, please follow the steps from [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems | this article]] to troubleshoot further. # If nothing from the above helps, try [[Manage Firefox profiles|creating a new Firefox profile]] and check if the issue persists there. If it doesn't, you can [[Restore bookmarks, passwords and data from an old Firefox profile|start copying files from your old profile to the new one]] to identify which one causes the issue. See [[About your important data and their files|this article]] on what files to copy. <!-- Some additional troubleshooting steps What kind of ETP setting do you have? To find out, go to ''about:preferences#privacy'' and let us know if you set it to Standard/Strict/Custom. '''Check if the issue is caused by Total Cookie Protection (TCP)''' <i>'''WARNING from the moderator team:''' ''Changing Firefox pref from the about:config page can sometimes break Firefox or cause strange behavior. You should only do this if you know what you're doing. Please read [[Firefox advanced customization and configuration options]] to learn more. '' </i> * Go to about:config and check if the pref “''network.cookie.cookieBehavior''” is set at 5, which means that TCP is enabled together with ETP. If the pref value is not 5, then the issue is not TCP-related. * Set the pref “''network.cookie.cookieBehavior''” to 4 and check if the issue still exists. If the issue disappears, then it is a TCP breakage. In that case, you can file a report through [https://mzl.la/anti-tracking-breakage Bugzilla] or reach out to the [https://matrix.to/#/#anti-tracking:mozilla.org #anti-tracking] team on Matrix. -->

its not ETP. cache deleted, cookies not deleted cause i have a lot of logins. troubleshoot mode still the same. i logged out from YT: works! logged in again: works. strange cookie problem maybe? thanks for help dear Konstantina!

Maybe but I would assume that would be fixed with troubleshoot mode. Anyways glad it helped, have a good one :)