Created attachment 556692 [details] testcase See testcase, with that, I get an extra taskbar entry in the Windows taskbar, with no title in there. So I guess that's from the plugin window.
Created attachment 558487 [details] [diff] [review] patch On Windows, SetParent(nsnull) strips the child attribute and sets the parent to the desktop. To avoid it showing up on the taskbar you also need to hide the window.
Fixed by backout.