On 1 out of 4 Windows 10 computers, Firefox's standard file dialog (open, save, etc) displays almost completely full screen and cannot be resized. The screen shot shows that Restore and Minimize are greyed out, indicating that the dialog thinks it is in "normal" mode. Things I have tried to no avail: - Alt-Space > Move or Size has no effect. The cursor does not change to the appropriate resize or move icon and the arrow keys do nothing. In fact, usually after pressing Alt-Space then selecting Move or Resize, the popup menu should disappear and then you are in the selected mode with the arrow keys. In my case the popup menu does not close, as if clicking or pressing enter on Move or Size is not even being recognized. - Using the mouse at any of the dialog edges or corners- the cursor changes to the appropriate resize shape, but the edge cannot be dragged. Trying to drag on the dialog title bar also has no effect. - Per some other threads I have tried deleting xulstore.json from my profile folder- no effect - Running Firefox in safe mode- no effect I am totally stumped on this and I don't usually stump easily. This was happening on this system with FFox 49, I just updated to 50 but still same issue. Thanks for any clues or advice!