I'm currently experiencing an issue in which websites and plugins don't display correctly on a new phone (Note 9)
I can't even configure add ons, it winds up looking like this (Ublock origin) https://ibb.co/jvYTZq
Restarting Firefox doesn't work but restarting the whole phone fixes it for a little while.
Addendum: Clearing the cache has no effect, Force closing the app seems to reset things adequately enough to get me running again.
Android 8.1.0, Firefox 63.0.2
Some functions won't do anything, like, the "Request Desktop Site" checkbox