Very useful, precise, and on top of that, open-source! And it doesn't abuse your personal data. Supports many languages

Très bonne extension, elle sait reconnaître en plus des fautes les langues. Parfait

Es un corrector molt ben parit i efectiu

Es el mejor corrector ortográfico que he usado. Excelente. 100% Recomendado

super!

Das Programm ist spitze, erleichtert mir meine schreib arbeit sehr, ein click und schon sehe ich meine schreib Fehler.

Eine wirklich sehr gutes Add-on. Es hat viele Sprchen zur Auswahl.

Da ich 91 Jährig nicht mehr die Möglichkeit habe andern eine Nachricht zu senden Danke ich Ihrer Firma. Ich werde meinen Beitrag leisten, wenn ich meine Zähne habe, aber das dauert noch.

I'm not using it for long, but it seems to work very well, it also helps in writing not only in fixing grammar errors, but also warns you about duplicate words and other little stuff (I guess the pro version is even better).
Not only it does work well, but is also very pleasant to look at, both the configuration page and the little pop up when you want to fix the words etc... I love the style!
Sadly it does not work in every fields, like for example Google search bar or the one where I'm writing the review! This is a little bit ironic

Edit to answer: I didn't know about mozilla limiting them on the site, but I think if it could be possible to have the spellcheck even for those text field (maybe with a settings to disable them?).

spiffy, straight forward & intuitive