works, but much worse privacy than the mozilla's recommended languagetool addon (https://addons.mozilla.org/en-US/firefox/addon/languagetool/)

Pretty much all spellchecker extensions now suffer from this problem, but about half of the suggestions I get nowadays are not helpful and about one-quarter are simply wrong.

Paid extension after a while.

It's ok overall - I use it through my university's account so I don't need to pay for it. That's the only reason I use it tbh. But, when I went to install the desktop version today, it opened Chrome to install there as if that was my default browser (which it is not!). In addition to that, the little bubble that pops up in Firefox can be incredibly annoying. In most cases, it either doesn't want to move out of the way of the text I'm typing so I can see what I'm typing, or it'll give me a suggestion that I'll click on and then it won't change anything! If I weren't getting the paid version through my school tuition, I would definitely not buy it or use the (very limited) free version.

Grammarly keeps disappearing though?

I like it!