diff --git a/browser/devtools/inspector/test/browser_inspector_scrolling.js b/browser/devtools/inspector/test/browser_inspector_scrolling.js
index c7fb0fdef73..6d81576f06a 100644
--- a/browser/devtools/inspector/test/browser_inspector_scrolling.js
+++ b/browser/devtools/inspector/test/browser_inspector_scrolling.js
@@ -42,6 +42,8 @@ function inspectNode(aInspector)
 function performScrollingTest()
 {
   executeSoon(function() {
+    // FIXME: this will fail on retina displays. EventUtils will only scroll
+    // 25px down instead of 50.
     EventUtils.synthesizeWheel(div, 10, 10,
       { deltaY: 50.0, deltaMode: WheelEvent.DOM_DELTA_PIXEL },
       iframe.contentWindow);
diff --git a/testing/mochitest/tests/SimpleTest/EventUtils.js b/testing/mochitest/tests/SimpleTest/EventUtils.js
index e73627abe65..932eb72b2e3 100644
--- a/testing/mochitest/tests/SimpleTest/EventUtils.js
+++ b/testing/mochitest/tests/SimpleTest/EventUtils.js
@@ -412,13 +412,6 @@ function synthesizeWheel(aTarget, aOffsetX, aOffsetY, aEvent, aWindow)
                   aEvent.deltaY > 0 ? Math.floor(aEvent.deltaY) :
                                       Math.ceil(aEvent.deltaY);
 
-  if (aEvent.deltaMode === WheelEvent.DOM_DELTA_PIXEL)
-  {
-    aEvent.deltaX *= devicePixelRatio;
-    aEvent.deltaY *= devicePixelRatio;
-    aEvent.deltaZ *= devicePixelRatio;
-  }
-
   var rect = aTarget.getBoundingClientRect();
   utils.sendWheelEvent(rect.left + aOffsetX, rect.top + aOffsetY,
                        aEvent.deltaX, aEvent.deltaY, aEvent.deltaZ,