It usually works, but recently, it started to say I needed to login when I already did.

Firefox and Grammarly are not a good marriage. I am going back to Chrome, it is better, works with no issues. Firefox is missing features. To see the mistakes I need to click and get a new window, while in Chrome it is fluently showing me the first level of errors.

I kept signing in this dumb Grammarly, but it keeps making me sign in over and over again and it couldn't work properly.

I loved it on the desktop but it doesn't work on Firefox for Android

Sometimes it interferes with some websites. Eg Microsoft Technet forums and it's a pain in the ass!

The *only way* is to open Menu > Add-ons > select this add-on > Disable it (temporarily)

It would be nice if there's a right-click shortcut to disable it temporarily.