By Adam Pash, 2:30 PM on Thu Mar 15 2007,
1. Make sure Firefox is closed.
2. Find your profile folder, which by default should look something like xxxxxxxx.default.
3. Inside your profile folder, find the file called persdict.dat and open it up in your text editor of choice.
4 Now just find the misspelling, delete it, and you're done.
as you can add more words to you personal dictionary as well just by adding 1 word per line see <a href="http://labnol.blogspot.com/2006/11/firefox-2-spelling-dictionary-hacks.html">http://labnol.blogspot.com/2006/11/firefox-2-spelling-dictionary-hacks.html
</a> for more info on how.