I am using Firefox 4.0 b11. I am getting this error (I translated it myself, so it might not be 100% accurate): Sync is unable to synchronise: Unknown error. Sync will attempt to try this action again. The error is shown just above the status bar, and contains a button with 'Synchronise now'. Also, when I go to the options, and try to edit my password, or login again, the buttons just don't work. Can someone help me with this? '''Edit:''' I partially solved the problem. I had an old Firefox Sync addon. I think it remained active since the upgrade from FF 3.6. But still, it seems that no synchronisation is happening. Shouldn't I get some sort of notice to indicate that the synchronisation has succeeded?