Grammarly is well worth the low cost for the complete version. It is usually accurate in performing the daunting task of finding and correcting grammatical errors. Its better than most. I use it all the time.

I've heard many others say this too, I cannot sign in.

I am not being able log into the Grammarly account in the add-on, in Firefox.

Doesn't work whatsoever.

I LOVE IT