Bookmarks are stored in the Firefox profile in the user library. The path is /Users/<username>/Library/Application Support/Firefox/Profiles/<randomname>.default

The easiest way to find the profile is to use Help > Troubleshooting Information and click the Show in Finder button.

I found it advisable to keep backup copies of the profile, and a separate copy of bookmarks as well. You should have 10 copies of bookmarks available to restore. Surely one of these is intact?

If you use the Time Machine then you can try to restore a copy of places.sqlite from just before this deletion.

If you have accidentally removed bookmarks then use "Organize > Undo" in the bookmarks manager (Bookmarks > Show All Bookmarks) to get them back.
The Organize button is the first of the three buttons on the toolbar in the Library (Bookmarks Manager).
That only works if you haven't closed Firefox.
If it didn't work then you can restore the bookmarks from a JSON backup.
This will replace all current bookmarks and you lose bookmarks that were added since that backup was created.

See:

• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

Thanks guys. Got it back! I appreciate the responses.