diff --git a/dom/events/test/test_bug574663.html b/dom/events/test/test_bug574663.html
index 64f0d6c69ed8..164fdcf41d73 100644
--- a/dom/events/test/test_bug574663.html
+++ b/dom/events/test/test_bug574663.html
@@ -48,8 +48,8 @@ function waitForPaint(win, utils, callback) {
 }
 
 // This is a magic number representing how many device pixels we are attempting to
-// scroll or zoom.  We use it for sending the wheel events, and for checking the
-// outcome of the events that are expected to trigger scrolling.
+// scroll or zoom.  We use it for sending the wheel events, but we don't actually
+// check that we have scrolled by that amount.
 var kDelta = 3;
 
 function sendTouchpadScrollMotion(scrollbox, direction, ctrl, momentum, callback) {
@@ -68,14 +68,15 @@ function sendTouchpadScrollMotion(scrollbox, direction, ctrl, momentum, callback
   // --- Intermittent Warning ---
   // Two wheel events are sent, but our promise resolves when any change has been
   // made to scroll or zoom. That makes it possible that the effect of the second
-  // event may not yet be applied when the promise resolves, which will lead to a
-  // failure when checking the expected value for scrolling. This was done
-  // intentionally, because attempting to wait after both events yields problems
-  // when the second event has no effect, which does happen in testing. It's
-  // not clear why this is happening. Since the testing pattern is scroll (twice),
-  // then scroll back (twice), it's possible that the first scroll back event is
-  // sufficient to return the scrollbox to its minimal scrollTop position, and
-  // therefore the second event doesn't scroll any further.
+  // event may not yet be applied when the promise resolves. This shouldn't lead
+  // to any errors, since the two wheel events are moving in the same direction,
+  // and our later checks will only ensure that the value has changed from its
+  // initial value. This was done intentionally, because attempting to wait after
+  // both events yields problems when the second event has no effect, which does
+  // happen in testing. It's not clear why this is happening. Since the testing
+  // pattern is scroll (twice), then scroll back (twice), it's possible that the
+  // first scroll back event is sufficient to return the scrollbox to its minimal
+  // scrollTop position, and so the second event doesn't scroll any further.
   const initialZoom = winUtils.fullZoom;
   const initialScroll = scrollbox.scrollTop;
 
@@ -143,7 +144,7 @@ function runTest() {
           let postfix = isMomentum ? ", even after releasing the touchpad" : "";
           // Normal scroll: scroll
           is(winUtils.fullZoom, zoomFactorBefore, "Normal scrolling shouldn't change zoom" + postfix);
-          is(scrollbox.scrollTop, scrollTopBefore + kDelta * 2,
+          isnot(scrollbox.scrollTop, scrollTopBefore,
              "Normal scrolling should scroll" + postfix);
         } else {
           if (!isMomentum) {
@@ -151,7 +152,7 @@ function runTest() {
             is(scrollbox.scrollTop, scrollTopBefore, "Ctrl-scrolling shouldn't scroll while the user is touching the touchpad");
           } else {
             is(winUtils.fullZoom, zoomFactorBefore, "Momentum scrolling shouldn't zoom, even when pressing Ctrl");
-            is(scrollbox.scrollTop, scrollTopBefore + kDelta * 2,
+            isnot(scrollbox.scrollTop, scrollTopBefore,
                "Momentum scrolling should scroll, even when pressing Ctrl");
           }
         }