I fixed it yesterday, but I really don't know why it worked...
In the DOM tab of Firebug, I saw a "menubar" entry, and changed the "visible" value from true to false by double-clicking on it (see file attached). Immediately the empty menu bar disappeared, and since this moment everything is OK (after restarting Firefox or rebooting my machine) though this value has come back to "true", obviously... I can't explain.
I fixed it yesterday, but I really don't know why it worked...
In the DOM tab of Firebug, I saw a "menubar" entry, and changed the "visible" value from true to false by double-clicking on it (see file attached). Immediately the empty menu bar disappeared, and since this moment everything is OK (after restarting Firefox or rebooting my machine) though this value has come back to "true", obviously... I can't explain.