Bug 868327 - Only allow the drop-down menu to open above the combobox if there is room for it, otherwise open it below even though it doesn't fit. r=roc

layout/forms/nsComboboxControlFrame.cpp

@@ -646,9 +646,10 @@ nsComboboxControlFrame::AbsolutelyPositionDropDown()
     return eDropDownPositionPendingResize;
   }
 
-  // Position the drop-down below if there is room, otherwise place it
-  // on the side that has more room.
-  bool b = dropdownSize.height <= below || below >= above;
+  // Position the drop-down below if there is room, otherwise place it above
+  // if there is room.  If there is no room for it on either side then place
+  // it below (to avoid overlapping UI like the URL bar).
+  bool b = dropdownSize.height <= below || dropdownSize.height > above;
   nsPoint dropdownPosition(0, b ? GetRect().height : -dropdownSize.height);
   if (StyleVisibility()->mDirection == NS_STYLE_DIRECTION_RTL) {
     // Align the right edge of the drop-down with the right edge of the control.