It's Alt in XFCE.Try Alt instead of shift. Alt is the default key for this in most distributions but it was changed to Shift in SuperZaxxon so that the shoulder button could be used for this.Moving is not working with shiftkey
- Neelix
You can easily change it in the XFCE setings.
It's in
Settings > Window Manager Tweaks > Accessibility
(I hope You're using XFCE. Else it's useless)