--- a/dom/base/test/file_domwindowutils_animation.html
+++ b/dom/base/test/file_domwindowutils_animation.html
@@ -80,19 +80,20 @@ function test_getUnanimatedComputedStyle
         }
         checkUnanimatedComputedStyle(property, initialStyle, null,
                                      expectedInitialStyle,
                                      expectedDuringTransitionStyle,
                                      cssTransition, "CSS Transitions");
       }
 
       addStyle([cssAnimationStyle,
-                ".pseudo::before { animation: cssanimation 1s; content: ''}"]);
+                ".pseudo::before { content: '' }",
+                ".animation::before { animation: cssanimation 1s }"]);
       const pseudoAnimation = target => {
-        target.classList.add("pseudo");
+        target.classList.add("animation");
         return target.getAnimations({ subtree: true })[0];
       }
       checkUnanimatedComputedStyle(property, initialStyle, "::before",
                                    expectedInitialStyle, expectedInitialStyle,
                                    pseudoAnimation, "Animation at pseudo");
       deleteStyle();
     });
   });
@@ -126,16 +127,19 @@ function checkUnanimatedComputedStyle(pr
                                       expectedDuringAnimation,
                                       animate, animationType) {
   const div = document.createElement("div");
   document.body.appendChild(div);
 
   if (initialStyle) {
     div.style[property] = initialStyle;
   }
+  if (pseudoType) {
+    div.classList.add("pseudo");
+  }
 
   is(utils.getUnanimatedComputedStyle(div, pseudoType, property),
      expectedBeforeAnimation,
      `'${ property }' property with '${ initialStyle }' style `
      + `should be '${ expectedBeforeAnimation }' `
      + `before animating by ${ animationType }`);
 
   const animation = animate(div);