Sync mostly occurs when Firefox is idle, but you can try speeding it up by clicking Sync Now. If you still don't see the other bookmarks, you can check what data is in the Sync cloud for your Mozilla Account using the About Sync add-on: https://addons.mozilla.org/firefox/addon/about-sync/ After you install the add-on, you can type or paste '''about:sync''' in the address bar and press Enter to load it. The page shows each category of data currently found in the Sync cloud. Anything useful under bookmarks? If not, do you still have access to your old PC or did you make any backups of the data on it?