--- a/dom/base/test/file_domwindowutils_animation.html
+++ b/dom/base/test/file_domwindowutils_animation.html
@@ -92,31 +92,36 @@ function test_getUnanimatedComputedStyle
       }
       checkUnanimatedComputedStyle(property, initialStyle, "::before",
                                    expectedInitialStyle, expectedInitialStyle,
                                    pseudoAnimation, "Animation at pseudo");
       deleteStyle();
     });
   });
 
+  const div = document.createElement("div");
+  document.body.appendChild(div);
+
   SimpleTest.doesThrow(
     () => utils.getUnanimatedComputedStyle(div, null, "background"),
     "NS_ERROR_INVALID_ARG",
     "Shorthand property should throw");
 
   SimpleTest.doesThrow(
     () => utils.getUnanimatedComputedStyle(div, null, "invalid"),
     "NS_ERROR_INVALID_ARG",
     "Invalid property should throw");
 
   SimpleTest.doesThrow(
     () => utils.getUnanimatedComputedStyle(null, null, "opacity"),
     "NS_ERROR_INVALID_ARG",
     "Null element should throw");
 
+  div.remove();
+
   next();
   window.close();
 }
 
 function checkUnanimatedComputedStyle(property, initialStyle, pseudoType,
                                       expectedBeforeAnimation,
                                       expectedDuringAnimation,
                                       animate, animationType) {