Installing Firefox's Spell checker

I've often wanted a spell-checker when writing Squidoo lens etc.

Am I the only who didn't know you can install a spell checker in Firefox?

Firefox's Spell checker is an Optional Plug-in! When writing your blog or
squidoo lens right-mouse click and select "add
dictionaries". Thereafter misspelt words will be underlined. Curiously the American dictionary I installed didn't contain "Firefox"

As soon as I installed it I started noticing small typos and British spelling in my popular lens http://www.squidoo.com/creatingideas Just How do you Create More Ideas?