https://www.reddit.com/r/Monitors/comments/ye5ii6/since_nobody_posted_about_this_firefox_doesnt/
Since nobody posted about this, Firefox doesn’t support High Refresh Rate despite the toggle existing, chromium browsers do. What can I do to use my monitor to the fullest with Firefox?
Since nobody posted about this, Firefox doesn’t support High Refresh Rate despite the toggle existing, chromium browsers do. What can I do to use my monitor to the fullest with Firefox?
And yes, I did visit this article already, did Not work 
How to Change Firefox Frame Rate for High Refresh Rate Monitor | UbuntuHandbook