I have no issues with YT. see screenshot https://www.youtube.com/watch?v=BBgeapTTWGk Can you show us the issue? Did you try with Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf You could also try Refreshing Firefox. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings What security software are you running? If running Pro version of Windows, I suggest enabling this feature to test. How to Use Windows 10's New Sandbox (to Safely Test Apps) https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

I found out that when opening a you tube video it opens paused, (it never happened before) when I clicked the space bar or the K key it plays. Do you know why the videos open paused?

Default autoplay settings make videos with sound (ie not muted) load paused in tabs that have not been interacted with. You can change the default to "Allow audio and video" if you want them to always play.

auto play was already set to ALLOW, it did not make a difference. see screenshot