--- a/widget/tests/test_keycodes.xul
+++ b/widget/tests/test_keycodes.xul
@@ -231,17 +231,19 @@ function runKeyEventTests()
           return testingEvent.capsLock && removeFlag(e, kCapsLockFlag) && expectedDOMKeyCode != e.keyCode;
       }
       return false;
     }
 
     // Ignore the state changing key events which is fired by the testing event.
     if (!isStateChangingModifierKeyEvent(e))
       eventList.push(e);
-    e.preventDefault();
+    if (e.type == "keypress") {
+      e.preventDefault();
+    }
   }
 
   const SHOULD_DELIVER_NONE             = 0x0;
   const SHOULD_DELIVER_KEYDOWN          = 0x1;
   const SHOULD_DELIVER_KEYPRESS         = 0x2;
   const SHOULD_DELIVER_KEYUP            = 0x4;
   const SHOULD_NOT_CAUSE_INPUT          = 0x8;
   const SHOULD_DELIVER_ALL              = SHOULD_DELIVER_KEYDOWN |