We are actively investigating the issue here. This issue was introduced with Firefox 65.0.2. We haven't done a release in about a month on Firefox. Here is the bugzilla ticket if anyone wants to follow along: https://bugzilla.mozilla.org/show_bug.cgi?id=1535589
We could use your help in diagnosing the problem: If you could go to `about:crashes` in Firefox and send us the crash ID from the crash report to email@example.com, that would be such a help!
It's buggy, crashes/slows things down, but what I dislike the most is its complete lack of support for customization. Really, if I can't make adjustments (without basically hacking it that is) then I don't want it.