What do you do about misspelling words in text boxes?  Well, you use the built-in Firefox spell check feature.  However, by default it does not work with ALL text fields.  That can simply be rectified though your about:config settings.

Just type in about:config into your address bar to get started.  Next, into the filter text box, type in layout.spell.  That should bring up the preference name layout.spellcheckDefault. Right-click it, and then select “Modify”.  Change the 1 (default value) to 2 [...]