Lo uso mucho

Fabulous!

Muito util

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

I like that it still allows custom sources.

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

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.