Mozilla: work space margins and taskbar autohide

[Jack Kern]

Mozilla seems to pay no attention to the Work Space Margin settings.  If 
I use Autohide for the Taskbar, Mozilla even places itself such that the 
unhidden taskbar covers Mozilla's title bar.  If Taskbar/Autohide is 
off, Mozilla stops at the margin of the task bar.  (Although Mozilla 
shows no option for X geometry position but only for size, "-width" and 
"-height", xfce4-session puts it in the saved position every time.)