I just discovered a very very useful extension for Firefox, Spellbound, a spelling checker for anything you type into a web form.
What's shameful is that this is not listed on any of the usual Firefox extension sites, neither Texturizer, Extension Room nor Firefox Update list it. And it's so useful it should probably be a part of the basic browser. One more example of open source's tendency of smashing it's own toes with glee!
(Now you have no excuses for bad spelling)