Commenting to hopefully boost this up in support priorities - I also just found out I have this issue as of today. Tried refreshing firefox, going back in an update, etc and nothing worked. This happens when I go full screen in websites like Netflix or Hulu but not Youtube for some reason.

I have the same or similar problem with my screen dimming. My observations so far: Dims in Firefox, but not Safari OK in small screen, but not full screen Doesn't happen if cursor left on progress bar at the bottom Using subtitles, doesn't happen when subtitles up, but dims when they disappear, then brightens at next subtitle No difference whether connected to power or not This has just started happening for me in the last couple of days. No issues before that

Some websites have a dimmer option during playback. Make sure this is turned off.

Make sure you are not blocking content.

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/

https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

The issue of screen dimming when going to full screen only happens with Firefox. Does not happen with Safari using identical streaming sources.I can no longer use Firefox to stream video if I want to view in full screen, seems the problem is in Firefox as Safari works fine.

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address box.