I've used FF to checkout Outlook email and it does spellchecker.

Hi frustratedandlost, does the spell checker work for you on others sites, such as this one? This one has very simple form controls compared with email sites, but the principle is the same.

Could you check:

(1) right-click the editing area, make sure there is a check mark for "Check Spelling" and, if there is not, click that to turn on spell checking

(2) right-click, expand Languages, and make sure you have the language you want checked

If it doesn't appear, you may need to add a dictionary. See How do I use the Firefox spell checker? (third section of the article)