Comment 19 for bug 363983

Try the following
when on single desktop run

xrandr

It will return something like

Screen 0: minimum 320 x 200, current 2880 x 900, maximum 2880 x 900
default connected 2880x900+0+0 0mm x 0mm
   2880x900 60.0*
   2560x800 60.0
   1440x900 60.0
   1280x800 60.0
   1280x768 60.0
   1024x768 75.0 70.0 60.0
   800x600 75.0 72.0 60.0 56.0
   640x480 75.0 72.0 60.0
   640x400 75.0 60.0
   512x384 75.0 60.0
   400x300 75.0 60.0
   320x240 75.0 60.0
   320x200 75.0 60.0

As I know for a single screen is should actually be set to

   1280x800 60.0 *

Not

 2880x900 60.0*

You then run

 sudo xrandr --output default --mode 1280x800

Which then allows thunderbird to start
(kill any background thunderbirds started with the wrong screen resolution first)