We had an interesting problem occur today when we started up one of our Macs and launched Safari. All of the bookmarks that usually display in the Bookmarks Bar were gone. The bookmarks in the Bookmarks Menu had disappeared, too.
Courtesy of Apple
This happened after the Apple Mail app got hung up for some reason. We had to use the Force Quit option to get out of Mail, but we had no trouble manually quitting Safari and the other apps we had open at the time. When we rebooted the Mac and launched Safari, everything had disappeared. There wasn't a single item in the Bookmarks Bar or the Bookmarks Menu.
Restoring the bookmarks wasn't a problem. We have another Mac that has the same bookmarks, so we just moved them over. If you're not sure how to move bookmarks, you'll find instructions here:
We could also have restored the bookmarks from a Time Machine backup or from iCloud, but the other Mac happened to be on and mounted on the Desktop, so copying the bookmarks seemed like the easiest solution. We still haven't figured out what happened, though.
If you haven't backed up your bookmarks lately, take a moment to do so now. It's easy, and you'll find instructions in the guide above.