Look on your desktop. Do you see a folder called; Old Firefox?

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

In the address bar, type about:crashes<enter>. Note: If any reports do not have BP- in front of the numbers/letters, click it to submit them.

The crash report is several pages of data. We need the report numbers to see the whole report.

Using your mouse, mark the most recent 7 - 10 crash reports, and copy them. Press the Reply button. Now go to the reply box and paste them in.

For more help on crash reports, see; https://support.mozilla.org/en-US/kb/firefox-crashes-asking-support

No, there is no old firefox folder on my desktop

Any crash reports?

Type about:profiles<enter> in the address bar. How many profiles are listed? How many should be there?

You might consider shutting down your Mac and starting it back up again to release locked files before doing a lot more exploring.

Then, if that doesn't restore sanity, could you investigate:

Does the Profile Manager list your immediately previous profile folder?

To check on that, inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

This page should list all the profiles Firefox is currently aware of. If you see a profile that is not currently set as default that looks promising, scroll down to it and click the Set as default profile button below that profile, then scroll back up and click the Restart normally button. (There are some other buttons, but I think those are still "under construction" so please ignore them.)

Firefox should exit and then start up using the other profile. Is that the right one?

If it's not there...

Did Firefox orphan your old profile folder?

Here's how to check whether there are additional profile folders in the standard location in addition to the one you're using. Start by opening your current Firefox profile folder using either:

* "3-bar" menu button > "?" button > Troubleshooting Information
* (menu bar) Help > Troubleshooting Information
* type or paste about:support in the address bar and press Enter/Return

In the first table on the page, click:

* Windows: the "Open Folder" button, to launch a new window listing various files and folders in Windows Explorer.
* Mac: the "Show in Finder" button, to launch a new window listing various files and folders in Finder.

In the Windows Explorer address bar, click the capitalized word Profiles to move up one level in the folder hierarchy. More than one folder here by any chance? Do the files in those folders look like they were last updated around the time of the crash?

(Mac users: please do what you need to do in Finder to check up one level...)

If you've got any promising looking folders, we can discuss next steps to recover use of them.

o.k. I restarted my computer and I now see a folder "Old Firefox Data" on the desktop. There are a lot of files in it - what do I do now?

Great ! ! Use the file browser to open the folder. Look for the newest dated folder. That would be the profile you were using before.

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

What do you mean by "use the file browser to open the folder"?

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Go to that message, and use the Undo link to its right.

Whatever/however Mac users look thru their hard drives, do it.

If your interest is limited to bookmarks, use the built-in Restore feature and if there are no dated backups listed on the restore menu, use Choose File to go to the desktop, into Old Firefox Data, and into your old profile folder and look for a folder named bookmarkbackups to select a recent backup to restore to your new profile. Hopefully that will make sense in combination with this article:

Restore bookmarks from backup or move them to another computer