How to fix an upgraded Firefox profile

I'm an idiot. I ran a new version of Firefox nightly without creating a new profile. When I went to run my regular Firfox, I got this error message:

Using an older version of Firefox can corrupt bookmarks and browsing history already saved in your existing FireFox profile. To protect your information, create a new profile for this installation of firefox.

Here's how I fixed it.

  1. Close down Firefox
  2. Open a terminal and run:
  3. firefox --allow-downgrade
  4. Let Firefox start up and create a new profile. Then go to:
  5. about:profiles
  6. You'll see something like this:
    Screenshot of the profiles screen.
  7. Select "Set as default profile" and click through any warnings
  8. Close Firefox.
  9. Once again, run firefox --allow-downgrade

That should do it! Next time you start Firefox normally, everything should be fine. Probably.

In the future, make backups of your $HOME directory, and create a new profile for your Nightlies!

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