How to Edit the Firefox Custom Dictionary

Oooops! Didn’t really mean to add that particular word to the Firefox custom dictionary. Better remove it now before it causes problems later on..

As one who takes full advantage of the custom dictionary in Firefox, I occasionally find myself adding nonexistent or misspelled words to the dictionary by accident. Not wanting to deal with a false negative down the road, I always take the time to stop what I’m doing, locate the custom dictionary, and remove the erroneous term. Finally getting sick of trying to remember the esoteric location in which Firefox stores the personal dictionary, I decided to make a few notes and post the information here for easy access when it happens again (and it will happen again;).

Turns out that the location of the custom dictionary varies depending on your operating system. The name of the custom dictionary is “persdict.dat” (short for “personal dictionary”), and is located in the following location (depending on operating system):

Windows Vista


Windows XP

C:\Documents and Settings\[username]\ApplicationData\Mozilla\Firefox\Profiles\[unique-alphanumeric-string].default\persdict.dat

Mac OS X

~/Library/Application Support/Firefox/Profiles/[unique-alphanumeric-string].default/persdict.dat



Of course, the [username] (for Windows) and [unique-alphanumeric-string] will vary depending on your unique configuration. Once you have located the target file, “persdict.dat”, open it with a text editor and edit according to your needs. The file itself is simply a list of words that you have chosen to add to the dictionary by right-clicking in Firefox and selecting “Add to dictionary”. With this file, you can add as many custom words as you like, or, conversely, remove all those nefarious little rascals that you added by accident! Save, close, and done. Even so, why hasn’t somebody written an official “custom dictionary editor” extension for Firefox? Would be so nice!