I stopped using FF when I left my previous job, synced up my bookmarks before I left but then was unable to retrieve them because I had not written down the access guid. I'll just sync with my Google account and be done with it!
Having been a user and developer for almost any time, I would never have relied on that! A simple bookmark export, spot check for some URLs, USB drive/email/FTP to somewhere. I've always done that when leaving jobs (along with other personal things or notes/application settings).
Maybe I'm too cautious, but I've always ended up with a good copy of my data.