I accidentally added a word to my Firefox dictionary today, and after a quick Google Search I found this article.

Basically you need to find the persdict.dat. It can be found here in the following operating systems:

Windows XP

C:\Documents and Settings[User Name]\Application Data\Mozilla\Firefox\Profiles\xxxxxxxx.default\

Windows Vista

C:\users[User Name]\AppData\Roaming\Mozilla\Firefox\Profiles\xxxxxxxx.default\

Mac OS X

~/Library/Application Support/Firefox/Profiles/xxxxxxxx.default/



After you have located persdict.dat, open it in your favorite text editor and simply remove the misspelled word.