pcd2k, I am not familiar with Macs, and the following is written with Windows in mind. But hopefully you can adjust where needed.

It may be the case that Firefox has created a new profile, but your original profile still exists with all your bookmarks and other data, on your hard drive.

Do you, for example, have a folder named "Old Firefox Data" on your desktop? Firefox would create this folder as a copy of your old profile folder if it refreshed.

Firefox will also, by default, save profile folders in the following directory: C:\Users\<your Windows login username>\AppData\Roaming\Mozilla\Firefox\Profiles)

If Firefox has created a new profile, and you knew the location of the old profile folder, then you could restore your original data by following the steps in this article: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

(But you may wish to backup your new profile, as explained in the article, before attempting a restore. And to also backup the old profile folder before the restore)

You could also try just copying individual files from the old profile to the new profile (while Firefox is not running).

See the section "Your important data and their files" here, for the files to copy: https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile#w_your-important-data-and-their-files

(see the previous post for ideas on where to find the new and old profile folders, and I would once again advise to keep backups of all files that will be transferred or replaced)