Initially implemented in bug 731541, this was removed from that patch to allow it to land before bug 738501 is completed.
Created attachment 614917 [details] [diff] [review] Patch
Comment on attachment 614917 [details] [diff] [review] Patch myk r+'ed this change in bug 731541
Verified that this feature has landed in Windows. Followup problems detected will be tracked in separate bugs in the web apps component.