Mozilla released Firefox 67.0 recently and integrated in that release came a -- long-overdue -- feature that assigned unique profiles to each Firefox installation on the system.
The change should not have affected existing Firefox installations and profiles on the system but reports are coming in from all over the Internet that this is not the case for some users of the browser.
Mozilla's implementation assigns a unique profile to any new Firefox installation. That is a good thing for systems with multiple Firefox installations as you don't have to create and assign profiles for these installations manually anymore using the profile manager or other means.
Firefox uses the set profile from that moment on during start so that it is no longer necessary to tell the browser what to do (either manually on start or by using shortcut parameters).
Some Firefox users who upgraded the browser to version 67.0 noticed that it started with a blank profile; all their user data, bookmarks, open tabs, passwords, history, and other data appeared gone.
The problem that these users experienced is that Firefox assigned a new default profile to the installation; this should not have happened, but it appears to have happened to some.
Good news is that the user data is not deleted or gone. All that is needed is to assign the old profile to the installation of Firefox to restore it.
You have two main options to do so, one uses the Firefox interface to change the assigned profile, the second loads it using a parameter that you add to the Firefox shortcut.
The second option forces Firefox to load a specific profile or the profile manager on startup.
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