Bug 1273129 - Fix typo from physical to logical conversion (in bug 1113206). r=jfkthame

layout/forms/nsComboboxControlFrame.cpp

@@ -595,8 +595,8 @@ nsComboboxControlFrame::GetAvailableDropdownSpace(WritingMode aWM,
                                containerSize);
     mLastDropDownAfterScreenBCoord = thisScreenRect.BEnd(aWM) +
                                      aTranslation->B(aWM);
-    mLastDropDownBeforeScreenBCoord = thisScreenRect.BEnd(aWM) +
-                                     aTranslation->B(aWM);
+    mLastDropDownBeforeScreenBCoord = thisScreenRect.BStart(aWM) +
+                                      aTranslation->B(aWM);
   }
 
   nscoord minBCoord;