It works well, but you can't exclude the language from fixing.
Also, you can't ignore the same rule in different languages. For example, the rule is that a sentence doesn't start with an uppercase letter. I clicked 'ignore that rule' in English, but in Russian, it still works, and the 'ignore the rule' button doesn't work.

Extension très pratique à la rédaction de formulaire, corrige orthographe et grammaire.

Очень хорошее дополнение для браузера, отлично исправляет ошибки в тексте.

Not very good and over-complicatef

I meant complicated of course but this rubbish app didn't pot th error

If I can't install a different spell-checker on Firefox I'm going to use a different browser, that will be a shame.

Edited to add: Despite the Developer's response my opinion stands that this add-on is useless. Fortunately I have found an alternative that works perfectly.

Superior typiiing experience with ths addon even with broken keyboard liike I have. (no edit)

But autocorrection would be nice because theres so many errors with my keyboard.