I had been using FF 3.6 on 2 PCs untill yesterday, and only the native browser on an Archos 101 IT Android tablet. I have - upgraded 1st PC (Win. XP) to FF4 - added FF mobile to the android tablet, - synched both : OK. Then, - upgraded 2nd PC (Win 7) to FF4, - synched with previous. Problems : 1. on the 1st PC (Win XP), I still have an equivalent of the old horizontal menu (File, Edit, Display, History, Bookmarks, Scrapbook, ?) Is this normal ? There is no 'Tabs on top" option. 2. on the 2nd PC (Win 7, with the new Firefox button and, whenever Sync is active, I get the unknown error : (translated from french) Sync has encountered an error while synchronising : '''unknown error'''. Sync will automatically try this action again. I have stopeed and restarted Sync : same. The Personal Bar shows multiple copies of a single button (which existed before on both PCs, once only). I cannot delete any of these button copies. 3. on the same, I see History when pressing Ctrl+H (OK), but no bookmark when pressing Ctrl+B (empty). The Library (Ctrl+Shift+B) is also totally empty : no history, no bookmark. Some bookmarks show (copied from 1st PC, without my old bookmarks) in the Firefox > Bookmarks sub-menu. History is not synched. Bookmarks have disappeared from 2nd PC. I tried restoring from backups, but nothing showed. Anything I can do ? Thanks, Etienne