This add-on was once great! But now the sign-in button just takes me to my dashboard and does nothing else. I don't use Firefox for much of my writing, anyway.

Doesn't worn on Firefox.

Works for basic spelling and punctuation; not so good at advanced grammatical constructs--given that "grammar" is most of its name, that's a problem.

Appreciate the extra help to make sure my writing is professional!

Great for basic corrections. Very, very buggy for Wordpress websites. Some corrections do not take and adds junk code to your web pages. See this site for junk code example: https://searchfacts.com/grammarly-adds-junk-code/