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I want to back up all the words I've added to the Firefox Dictionary as its vocabulary is very limited. Where are they?

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  • Last reply by cor-el

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They just be stored somewhere, right? I looked in the profile files but of course there is nothing for dictionary there. That would be logical! So where is this little file? I sure don't want to go through adding hundreds of words again for my next install on another machine. And why is the Firefox dictionary so lacking in words? You'd think they'd just copy words over from any existing dictionary. It would be far better than it's present deficient state. All the time I have to add words it doesn't know.

They just be stored somewhere, right? I looked in the profile files but of course there is nothing for dictionary there. That would be logical! So where is this little file? I sure don't want to go through adding hundreds of words again for my next install on another machine. And why is the Firefox dictionary so lacking in words? You'd think they'd just copy words over from any existing dictionary. It would be far better than it's present deficient state. All the time I have to add words it doesn't know.

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Words you add to the dictionary are stored in persdict.dat in the Firefox profile folder.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).


You can backup certain files with Firefox closed from your profile folder to have a backup your personal data.

Note that best is to avoid restoring a full profile folder and only restore important files that are safe to restore/transfer.


  • bookmarks and history: places.sqlite
  • favicons: favicons.sqlite
  • bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
  • cookies.sqlite for the Cookies
  • formhistory.sqlite for saved autocomplete Form Data
  • logins.json (encrypted logins) and key4.db (encryption key/primary password) for logins saved in the Password Manager
  • cert9.db for certificates stored in the Certificate Manager
  • persdict.dat for words added to the spell checker dictionary
  • permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
  • sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

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