Sorry to hear about the data loss.

Did you ever sign up for the Firefox Sync service? That's the only scenario in which Firefox would have copied your bookmarks off your computer to the cloud.

If you created a Sync account before, you can try to add your new Firefox to your existing account. See: How do I set up Sync on my computer? - Section entitled "Connect additional devices to Sync"

Thank you for your reply. I've never heard of Firefox Sync before. I'm going to incorporate it from now on.

Was that the only way of getting my bookmarks back...?

Generally speaking, if you still have access to your hard drive, you can recover a local copy of bookmarks. If the hard drive is gone, then Sync is the only other built-in way to recover bookmarks.

There are other services out there for cloud sync, and various add-ons for backing up, but those would also have required you to set them up in advance.