Make link modifiers work consistently throughout Firefox
Reading through the bug it seems it make the following stuff:
Ctrl = new tab, selected
Shift = new window
Ctrl+Shift = new tab, in background
Alt = save
But you can checkout the patch yourself.
But most important a checkin was made with the following comment:
Fix a bug in EM compatibility checking code so that incompatible item details are shown. Before, a bad piece of control flow made sure that incompatible extension data was written into the datasource anyway, causing subsequent startup woes.
I really hope that takes care of the problems with Mozilla Firefox not starting!