Pressing the Red Button

If you accidentally add a misspelled word to your Firefox dictionary, here are the steps to remove it.

The words that you have added to your dictionary are stored in file called “persdict.dat”. It is located in your Firefox Profile directory.

To Get to your Firefox Profile Directory in Windows:
1. Click Start Menu -> Run, type “%APPDATA%”, then OK.
2. This will open your application data folder.

From there, the “persdict.dat” file is located in:
Mozilla\Firefox\Profiles\xxxxxxxx.default

Once there, you can edit the text file with notepad. There is one word per line. Remove the line to remove the misspelled word from your Firefox dictionary. Then save and restart Firefox.

Important Note: (before trying to remove a word)
If you have just added the word to your dictionary, it will not show up in the text file until you completely close all Firefox windows.

To Get to your Firefox Profile In Other Operating Systems:
The steps are the same for Firefox on other operating systems except for the location of the profile directory.
Mac:
~/Library/Application Support/Firefox/Profiles/xxxxxxxx.default/
Linux:
~/.mozilla/firefox/xxxxxxxx.default/

Additional Reference