diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 0a54b33f72a4..602db5fdbce9 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -2442,7 +2442,8 @@ void nsGfxScrollFrameInner::CurPosAttributeChanged(nsIContent* aContent)
                              -scrolledRect.y) +
            scrolledRect.y;
 
-  if (dest == GetScrollPosition()) {
+  // If we have an async scroll pending don't stomp on that by calling ScrollTo.
+  if (mAsyncScroll && dest == GetScrollPosition()) {
     return;
   }
 
diff --git a/layout/generic/test/Makefile.in b/layout/generic/test/Makefile.in
index abc329c5bace..ba253f4a6d7b 100644
--- a/layout/generic/test/Makefile.in
+++ b/layout/generic/test/Makefile.in
@@ -125,6 +125,8 @@ _TEST_FILES = \
 		test_bug589621.html \
 		test_bug589623.html \
 		test_bug632379.xul \
+		test_bug633762.html \
+		bug633762_iframe.html \
 		$(srcdir)/../../reftests/backgrounds/blue-32x32.png \
 		$(srcdir)/../../reftests/backgrounds/fuchsia-32x32.png \
 		$(NULL)
diff --git a/layout/generic/test/bug633762_iframe.html b/layout/generic/test/bug633762_iframe.html
new file mode 100644
index 000000000000..185d9af65a94
--- /dev/null
+++ b/layout/generic/test/bug633762_iframe.html
@@ -0,0 +1,8 @@
+<html>
+<body>
+<div style="background: red; height: 4000px;">hi</div>
+<div id="b" style="background: blue; height: 10000px;"></div>
+<div id="a" style="background: yellow; height: 100px;"></div>
+<div style="background: green; height: 4000px;"></div>
+</body>
+</html>
diff --git a/layout/generic/test/test_bug633762.html b/layout/generic/test/test_bug633762.html
new file mode 100644
index 000000000000..4b163026862b
--- /dev/null
+++ b/layout/generic/test/test_bug633762.html
@@ -0,0 +1,55 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=633762
+-->
+<head>
+  <title>Test for Bug 633762</title>
+  <script type="text/javascript" src="/MochiKit/packed.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+
+</head>
+<body>
+<p><a target="_blank" href="https://bugzilla.mozilla.org/show_bug?id=633762">Mozilla Bug 633762</a>
+
+<iframe id="i" src="bug633762_iframe.html#a"></iframe>
+
+<pre id="test">
+<script>
+
+var doc;
+
+function runTests() {
+  var i = document.getElementById("i");
+  doc = i.contentDocument;
+  var win = i.contentWindow;
+  // set display none on b
+  doc.getElementById("b").style.display = "none";
+  // flush layout
+  doc.documentElement.offsetLeft;
+  // click in middle of iframe document to give it focus
+  synthesizeMouseAtCenter(i, {}, win);
+  win.focus();
+  // record scrolltop
+  scrollTopBefore = doc.body.scrollTop;
+  // send up arrow key event
+  sendKey("UP", doc.body);
+
+  setTimeout("finish();", 0);
+}
+
+function finish() {
+  // assert that scroll top is now less than before
+  ok(scrollTopBefore > doc.body.scrollTop, "pressing up arrow should scroll up");
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.waitForFocus(runTests);
+</script>
+</pre>
+
+</body>
+</html>
