Easy fix via http://ubuntuforums.org/archive/index.php/t-1771058.html
find the line
<property name="<Super>Tab" type="string" value="switch_window_key"/>
and change it to
<property name="<Super>Tab" type="empty"/>
Or in terminal (via http://blog.zerosum42.com/2011/10/tech-fixing-tab-key-in-vnc.html):
xfconf-query -c xfce4-keyboard-shortcuts -p /xfwm4/custom/''Tab -r
For the last several days I got stuck in an annoying situation that I have to re-enter my account info (username and password) for every single website I use (about 10 I guess). For some reasons it seems that my newly-upgraded Firefox 3.5 Preview would not save any cookies at all.
So I did a little research the reason turned out to be some corrupted file called cookies.sqlite. All you have to do is to seek and destroy it. That’s all! (And by saying “destroy” I didn’t mean that you have to actually chop its head down or something, just delete it — even to the recycle bin is OK.) The file can often be found at your %appdata%\Mozilla\Firefox\Profiles\ and in a folder named whatever.default.
Hope this is helpful if you have the same bug with Firefox.