Bugzilla

I'm sorry to hear you're having similar issues.

Yes, the fix for this issue (as-reported) landed 2 years ago, in a supporting bug (as noted in Comment 28), which means Firefox 65 and newer include that fix.

So: whatever you're seeing, it's probably something different.

Could you please file a new bug, describing your use case & noting specifically which actions are slow (e.g. scrolling, typing) and any other info that seems relevant (e.g. does this only happen in WhatsApp threads with lots of backscroll)?

Also: ideally, it'd be great if you could capture a profile of the slowness, using https://profiler.firefox.com/ -- that site should give you an option to "enable profiler menu button", and then you can use that Firefox toolbar-button to start profiling, and then you can do the stuff that's unbearably slow, and then use the same toolbar-button to capture a profile.  Once you're looking at the profile UI, you can use the "share" button at the top-right of the profiler UI to upload and share the profile, and to get a permalink that you can post in the bug that you file.

(Note that the profile may show what other sites you have open in background tabs, so you may want to close background tabs to reduce noise & unrelated potentially-personal information that you might be sharing about what websites you're using.)

I'm sorry to hear you're having similar issues.

Yes, the fix for this issue (as-reported) landed 2 years ago, in a supporting bug (as noted in Comment 28), which means Firefox 65 and newer include that fix.

So: whatever you're seeing, it's probably something different (under-the-hood), even though it may have similar symptoms.

Could you please file a new bug, describing your use case & noting specifically which actions are slow (e.g. scrolling, typing) and any other info that seems relevant (e.g. does this only happen in WhatsApp threads with lots of backscroll)?

Also: ideally, it'd be great if you could capture a profile of the slowness, using https://profiler.firefox.com/ -- that site should give you an option to "enable profiler menu button", and then you can use that Firefox toolbar-button to start profiling, and then you can do the stuff that's unbearably slow, and then use the same toolbar-button to capture a profile.  Once you're looking at the profile UI, you can use the "share" button at the top-right of the profiler UI to upload and share the profile, and to get a permalink that you can post in the bug that you file.

(Note that the profile may show what other sites you have open in background tabs, so you may want to close background tabs to reduce noise & unrelated potentially-personal information that you might be sharing about what websites you're using.)