This is pretty common after a Firefox update, especially with YouTube because hardware acceleration, codecs, extensions, or cached site data can break after a browser change.

Try these in order (usually one of the first 4 fixes it):

1. Hard refresh YouTube Press Ctrl + F5 (Windows/Linux) or Cmd + Shift + R (Mac) Disable extensions temporarily Especially ad blockers, privacy tools, enhancer extensions, sponsor blockers, etc. Open: Menu → Add-ons and themes → Extensions Disable them all and test YouTube again.

Mozilla specifically notes extensions and ad blockers are a major cause of video playback failures.

2. Turn OFF hardware acceleration This is one of the biggest causes after Firefox updates. Open: Settings → General → Performance Uncheck: “Use recommended performance settings” “Use hardware acceleration when available” Restart Firefox

Recent Firefox releases have included fixes for YouTube/autoplay/video GPU issues, especially with NVIDIA and AMD cards.

3. Clear YouTube site data Go to: Settings → Privacy & Security → Cookies and Site Data → Manage Data Search for: youtube Remove all YouTube/Google entries Restart Firefox Update Firefox again Mozilla sometimes ships a quick patch right after a major update. Menu → Help → About Firefox Test Firefox Troubleshoot Mode This launches Firefox without extensions or custom GPU settings. Help → Troubleshoot Mode

If YouTube works there, the issue is definitely:

4. an extension GPU acceleration or a custom Firefox setting Check Enhanced Tracking Protection Sometimes strict privacy settings interfere with Google video scripts. Click the shield icon beside the address bar Turn protection OFF just for YouTube Refresh

Last resort: create a fresh Firefox profile Updates occasionally corrupt profiles.

Type: about:profiles Create a new profile Test YouTube there

i went through 3 steps. Refreshed the firefox browser and youtube videos played the rest of the day. The next day no more videos played on any site. I have to use chrome to watch any video files online.

Same problem, no video played in FireFox, but they played fine in Opera and the Mullvad browser.

Turning off hardware acceleration and deleting youtube cookies and restarting FireFox helped.

Thanks I love FireFox, will never use chrome.