Have you tried disconnecting Firefox Sync from your computer(s) and then logging back into Firefox Sync? This often fixes issues like this.

Some data on the Sync server like open tabs and history doesn't last forever and expires automatically, open tabs in seven days and history in sixty days. You should be able to get the bookmarks via Sync. ----- Did you make sure that you haven't switched profiles ? If you lost personal data then it is possible that a new default-release profile folder has been created. See "Determine if Firefox has created a new profile": *https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks *https://support.mozilla.org/en-US/kb/dedicated-profiles-firefox-installation