When you get the error bellow. These are the instructions to repair it.


STEP 1:

First we need to find our old user profile which was working fine in past and contains our browser data such as bookmarks, add-ons and settings.

Close Firefox and open RUN dialog box by pressing WIN+R keys together.

Now type firefox -p and press Enter key. It'll open Firefox in profile selection mode. Firefox will show a small dialog box to choose your user profile.

Select_User_Profile_Mozilla_Firefox_Launch.png

The box may contain 2 or more user profiles listed. For example, our Firefox installation contained following 2 user profiles:

  • default
  • default-release

"Default-Release" is the culprit. It's the new user profile created by Firefox automatically and Firefox is using this newly created profile as default.

Now select other profile such as "Default" and click on "Start Firefox" button. It'll launch Firefox with selected user profile.

If this is the old profile which contains all your previous browsing data, then move to STEP 2.

If this is not your previous user profile, close Firefox and again follow STEP 1 from beginning to launch firefox -p. Now check with other profiles listed one by one until you find your previous user profile.


STEP 2:

Now you know the name of your previous user profile in Firefox which stores all your bookmarks, add-ons and customized settings. Now we just need to set it as default so that Firefox starts using this profile by default.

Open Firefox and type about:profiles in address bar and press Enter key. It'll open Firefox Profile Manager. You'll notice all user profiles listed there which you saw on firefox -p dialog box.

Look for your previous user profile and click on "Set as default profile" button present below it.

Set_Default_Profile_Firefox_Profiles_Manager.png

That's it. Now Firefox will open with your old profile and you'll get all your bookmarks, add-ons, settings, history, etc back. Everything will be restored by Firefox and now you can use Firefox without any worries.

PS: The default i.e. currently selected profile will show "This is the profile in use and it cannot be deleted" message below its name.

NOTE: If you get "Another copy of Firefox has made changes to profiles. You must restart Firefox before making more changes" error message on about:profiles page, restart Firefox and the error message will disappear. If it still appears, restart your computer.