See:

• https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows
• https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues
• https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox

You can check the Web Console.

• https://firefox-source-docs.mozilla.org/devtools-user/web_console/

You can try to disable hardware acceleration in Firefox.

• Settings -> General -> Performance
  remove checkmark: [ ] "Use recommended performance settings"
  remove checkmark: [ ] "Use hardware acceleration when available"
• https://support.mozilla.org/en-US/kb/performance-settings

Close and restart Firefox after modifying the setting to make changes effective.

• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check if there is an update for your graphics display driver and check for hardware acceleration related issues.

• https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

Disabling hardware acceleration did the trick. However, when I play any YouTube video, my computer goes loud as it takes up so much CPU. In task manager, Firefox takes a whopping 25% CPU when I play a video. I don't think it's my computer that needs upgrading, because it's an i9-13900 with an RTX 4080. I cannot imagine why Firefox needs that much computational power from a 13th gen i9. And yes, I have all the latest updates (Windows, drivers, GPU drivers) installed.

What makes it so that running Firefox in troubleshoot mode allows hardware acceleration and work like other browsers? This is extremely frustrating as it seems to be only Firefox and I do not want to jump ship to Chrome or worse, Edge.