diff --git a/layout/generic/test/test_plugin_mouse_coords.html b/layout/generic/test/test_plugin_mouse_coords.html
index 7872d32a694..c9fb5c364ad 100644
--- a/layout/generic/test/test_plugin_mouse_coords.html
+++ b/layout/generic/test/test_plugin_mouse_coords.html
@@ -68,7 +68,7 @@ function doTest() {
 }
 // Need to run 'doTest' after painting is unsuppressed, or we'll set clip
 // regions to empty.
-addLoadEvent(function() { setTimeout(doTest, 0); } );
+addLoadEvent(function() { setTimeout(doTest, 1000); } );
 SimpleTest.waitForExplicitFinish();
 
 </script>
diff --git a/modules/plugin/test/testplugin/nptest.h b/modules/plugin/test/testplugin/nptest.h
index b68d32f3d42..e56ce11ec3e 100644
--- a/modules/plugin/test/testplugin/nptest.h
+++ b/modules/plugin/test/testplugin/nptest.h
@@ -94,6 +94,8 @@ typedef struct InstanceData {
   bool throwOnNextInvoke;
   uint32_t timerID1;
   uint32_t timerID2;
+  int32_t winX;
+  int32_t winY;
   int32_t lastMouseX;
   int32_t lastMouseY;
   int32_t widthAtLastPaint;
diff --git a/modules/plugin/test/testplugin/nptest_windows.cpp b/modules/plugin/test/testplugin/nptest_windows.cpp
index d9d5c43ac50..40c7c11c7f1 100644
--- a/modules/plugin/test/testplugin/nptest_windows.cpp
+++ b/modules/plugin/test/testplugin/nptest_windows.cpp
@@ -413,6 +413,17 @@ handleEventInternal(InstanceData* instanceData, NPEvent* pe, LRESULT* result)
     case WM_MOUSEWHEEL:
       return true;
 
+    case WM_WINDOWPOSCHANGED: {
+      WINDOWPOS* pPos = (WINDOWPOS*)pe->lParam;
+      instanceData->winX = instanceData->winY = 0;
+      if (pPos) {
+        instanceData->winX = pPos->x;
+        instanceData->winY = pPos->y;
+        return true;
+      }
+      return false;
+    }
+
     case WM_MOUSEMOVE:
     case WM_LBUTTONDOWN:
     case WM_LBUTTONUP:
@@ -420,8 +431,8 @@ handleEventInternal(InstanceData* instanceData, NPEvent* pe, LRESULT* result)
     case WM_MBUTTONUP:
     case WM_RBUTTONDOWN:
     case WM_RBUTTONUP: {
-      int x = instanceData->hasWidget ? 0 : instanceData->window.x;
-      int y = instanceData->hasWidget ? 0 : instanceData->window.y;
+      int x = instanceData->hasWidget ? 0 : instanceData->winX;
+      int y = instanceData->hasWidget ? 0 : instanceData->winY;
       instanceData->lastMouseX = GET_X_LPARAM(pe->lParam) - x;
       instanceData->lastMouseY = GET_Y_LPARAM(pe->lParam) - y;
       return true;