Wayne, Check out the link below.
http://spellbound.sourceforge.net/
More possibilities at the links at the search link below.
http://www.google.com/search?hl=en&q=spell+check+for+firefox&spell=1
Spell chicker for Firefox, like to spel check stuff like I'm typng now. Didn't I reed about it somwhere? An add-on for Firefox?
IE has a little utility called ieSpell that does this. If Firefox has it that's one step closer to me moving to FF.

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