I recently had to format my drive and wanted to recover my bookmarks from Firefox Sync. I had forgotten my recovery key, and had assumed I had not saved the key on the computer.
For this reason I generated a new key, which is currently synced under my account. The issue here is, I have just found the file containing my old key that corresponded with all my valuable data.
Is it impossible to retrieve all the data I had just lost with my old key?
No, that data is lost forever. However, if you still have the Firefox that is Sync with that account just resync it.
Thanks for the response, Tyler. I have the files for that version of Firefox. Is there a way I can take a bookmark file and copy it over to this newly-installed version, or something of the sort?
The bookmarks are stored in the places.sqlite file.
There are also JSON backups in the bookmarkbackups folder that you can use to restore and replace) all current bookmarks.