--- a/layout/xul/test/test_windowminmaxsize.xul
+++ b/layout/xul/test/test_windowminmaxsize.xul
@@ -194,17 +194,22 @@ function nextPopupTest(panel)
     setattr("maxwidth");
     setattr("maxheight");
 
     // Remove the flexibility as it causes the resizer to not shrink down
     // when resizing.
     if ("last" in popupTests[gTestId])
       document.getElementById("popupresizer").removeAttribute("flex");
 
-    panel.openPopup();
+    // Prevent event loop starvation as a result of popup events being
+    // synchronous. See bug 1131576.
+    SimpleTest.executeSoon(() => {
+      // Non-chrome shells require focus to open a popup.
+      SimpleTest.waitForFocus(() => { panel.openPopup() });
+    });
   }
 }
 
 function titledPanelWindowOpened(panelwindow)
 {
   var panel = panelwindow.document.documentElement.firstChild;
   panel.openPopup();
   panel.addEventListener("popupshown", () => doTitledPanelTest(panel), false);