It refuses to work with Google Docs. Every time I reinstall it says to signup. When I hit that it brings me to my Grammarly, but says it still isn't signed in at all. Plus the editing it does can be really stupid and change a sentence that doesn't need to be changed at all. Yea great app guys, it sucks. The minute it's actually good for something then let me know instead of spamming me ads on YouTube.

The "Show Definitions and Synonyms" option doesn't work.

Used this religiously back in the old days, and back with Waterfox. I've come back to Firefox Quantum 65, and while the addon works in 'guest mode', it does not register logging in to the Grammarly website.
The support staff has completely bent over backwards to try and help (thanks Irene and Tiffany!), but to no avail. I hope people have better luck with this than I have.

perfect, fast, free

best thing that happened in my life

xirotera