HOW TO: Remove misspelled words from your Firefox dictionary
We ain’t none of us perfect, so if you’ve ever accidentally added a misspelled word to your Firefox 
dictionary, here’s how to remove the misspelling to avoid looking like a fool in front of your friends, family, and coworkers: 1. Open your application data folder. On XP or Vista, go to your Start menu and hit Run (or just press Windows-R) and paste in %APPDATA%\Mozilla\Firefox\Profiles; on your Mac, navigate to ~/Library/Application Support/Firefox/Profiles.
Remove misspelled words from your Firefox dictionary - Lifehacker