Recently (it took me quite a while) I found firefox's spell checker - it's a great thing, but it's not enabled by default
Maybe it's not a bad idea to say a few words for guys that still do not use it (like me).
How to enable it:
Also by default, there are no dictionaries, how to install a few:
I installed Eng and BG, the bulgarian one works well enough:
Oddly enough, I had quite a lot of errors on the blog, by average 2 per blog entry. All fixed now.