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Firefox Dev doesn't launch with profile imported from Nightly

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  • Last reply by cor-el

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I've copied the root profile folder from my old machine, created a new profile running Nightly, put the contents of old profile into just created one, and it just worked. Doing the exact same steps with Dev version doesn't work - app refuses to launch after picking imported profile as default one. Could it be because Dev has a lower app version?

I've copied the root profile folder from my old machine, created a new profile running Nightly, put the contents of old profile into just created one, and it just worked. Doing the exact same steps with Dev version doesn't work - app refuses to launch after picking imported profile as default one. Could it be because Dev has a lower app version?

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Downgrading a profile is not officially supported and can produce unpredictable results but you can override it with the --allow-downgrade command line argument.

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Note that you shouldn't use a Nightly profile with a release version as those are not compatible. Instead you can transfer important data files.


  • 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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