If you use google as a search engine, you can consult here:

www.google.com/history

Automatically all the URLs visited not only from the computer, but from all the devices that have made searches from the same Google account appear.

As you found out, this Forget button is meant as a panic button to quickly close all open windows if you feel somehow guilty and want to hide what you are doing and you should use it with very much care.

• https://support.mozilla.org/en-US/kb/forget-button-quickly-delete-your-browsing-history

Using this feature clears all session data stored in sessionstore-backups folder and you would need to have a backup of sessionstore.jsonlz4 or files in the sessionstore-backups folder.

I would advice to remove this button from the toolbar (right-click -> Remove from Toolbar) if you do not really have a use for it and use "Clear Recent History" (Ctrl+Shift+Delete) instead.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

You can look at a utility to browse System Restore points to see if you can find an older copy of sessionstore.jsonlz4.

• https://www.shadowexplorer.com/
• https://www.nirsoft.net/utils/shadow_copy_view.html

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Thank you so much! Shadowcopy was particularly helpful; I have never heard of them but their program does exactly what it says it does.

Edit: I've found a copy of the sessionstore backups, but I'm unsure on how to actually use them to restart my session. Using the url scrounger just brings up 3 websites I haven't opened for years, which is decidedly odd.