[Update]
I guess they were listening to my original reply - they just pushed 2 updates very quickly, hooray.

[Original reply]
I've fixed all these issues in my local version but it's been taking almost a month for the Firefox team to approve my updates - whereas in Chrome it takes 30 minutes!

More info:
https://jasonsavard.com/forum/discussion/3198/issues-with-firefox#latest

I'll have to refer you to the Chrome extension until they approve the update. Just to give you an idea the Chrome extension is already 10 versions into the future https://jasonsavard.com/wiki/Checker_Plus_for_Gmail_changelog

I've had to reduce the compatibility back to Firefox 52 please don't rate me on this but rather the Firefox approval process.