A huge thank you to the person who wrote a review below. I've been using this extension for five years, and in the latest version, either there's an unintentional bug, or the developers intentionally introduced a leak that hadn't existed for 10 years.
This extension is currently causing a memory leak in the browser, even when I'm not opening anything and only on one page. It reaches 60 gigabytes for me, after which everything in the OS starts crashing with errors, from the browser to other programs.

I've been racking my brains for 2-3 weeks of torment, I couldn't figure out what was going on, because I've been using all the extensions for years and everything has been working without a hitch for a long time.
And it turns out that's what it is. The extension, which had been reliable for years, is now leaky and buggy, leaking 40-60 gigs of memory.
As soon as I removed this extension, everything has been fine for several weeks now.

Much more through and intuitive than any other grammar and spell checker I have used.

This is a great tool, however it needs some improvements. The button that is displayed when the user types in the text field, overlaps with the button displayed by another add-on - "DeepL: AI translator and writing assistant". Can this be fixed?

I like that it still allows custom sources.

Really nice, and for me at least, it even seems to be free!

I've been using LanguageTool for almost three years, and until recently I would have happily given it 5 stars.

Unfortunately, the recent changes to the free version have made the extension almost unusable for me. After the initial Premium trial ends, the extension no longer functions as a grammar checker, which completely defeats the reason I installed it in the first place.

I'm not giving 1 star because the software itself is bad. Quite the opposite — that's exactly why these changes are so disappointing. LanguageTool used to be an excellent free writing assistant, but now I'll have to look for an alternative.

I understand that developers need to make money, but the free version has become so limited that, for me, it has lost the value that made it worth installing.

This is a very useful add-on to Firefox. It's much more than a spelling checker, having a very good grasp of grammar and a reasonable ability to determine which word you meant to type. It's not perfect, but it's an excellent tool, as long as you don't follow it blindly.

Très utile.

El millor corrector de català del món.