On further investigation my passwords are not gone (though portions of the login information is), and strangely my "other bookmarks" folder is in place, but my main set of bookmarks is gone. "Import bookmarks" only gives me options relating to other browsers. So I would still like to undo this.

Restore Bookmark Backups Firefox automatically makes backups of the bookmarks. These are stored in the '''bookmarkbackups''' folder. Open the '''Bookmarks Manager; ''' Press the '''Alt''' or '''F10''' key to bring up the toolbar, and select '''Bookmarks. ''' Hot key is '''<Control> ''(Mac=<Command>)'' <Shift> B. ''' Firefox 84+ '''<Control> ''(Mac=<Command>)'' <Shift> O. ''' Once the window is open, at the top of the page, press the button labeled '''Import and Backup. ''' Select '''Restore. ''' From the list, pick the file you want and click it. The backups are stored in a '''jsonlz4 file''' named something like this; bookmarks-2016-06-29_1424_enD1GTH ya0JmicnYWg4V4g==.jsonlz4 In this example; 2016-06-29 = date created, 1424 = number of entries. https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks https://support.mozilla.org/kb/forum-response-recover-bookmarks-after-update