diff --git a/layout/generic/test/plugin_clipping_helper.xhtml b/layout/generic/test/plugin_clipping_helper.xhtml
index 371b6ba2d50..b9306d62362 100644
--- a/layout/generic/test/plugin_clipping_helper.xhtml
+++ b/layout/generic/test/plugin_clipping_helper.xhtml
@@ -2,8 +2,6 @@
 <?xml-stylesheet href="/tests/SimpleTest/test.css" type="text/css"?>
 <html xmlns="http://www.w3.org/1999/xhtml" title="Test Plugin Clipping">
 <head>
-  <script type="application/javascript" src="/MochiKit/packed.js"></script>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
   <style>
   embed { width:200px; height:200px; display:block; }
   iframe { border:none; }
@@ -50,6 +48,9 @@ function runTests() {
   checkClipRegion("p3", [[100, 100, 200, 200]]);
   checkClipRegion("p4", [[100, 100, 200, 200]]);
   checkClipRegionForFrame("f1", "p5", [[100, 100, 200, 200]]);
+
+  window.opener.SimpleTest.finish();
+  window.close();
 }
 ]]>
 </script>
diff --git a/layout/generic/test/plugin_clipping_helper2.xhtml b/layout/generic/test/plugin_clipping_helper2.xhtml
index 168355ee958..02632e7bcc8 100644
--- a/layout/generic/test/plugin_clipping_helper2.xhtml
+++ b/layout/generic/test/plugin_clipping_helper2.xhtml
@@ -33,12 +33,12 @@
 <script class="testbody" type="application/javascript">
 <![CDATA[
 var scroll = document.getElementById("scroll");
+var zbox = document.getElementById("zbox");
+var sbox = document.getElementById("sbox");
+var p1 = document.getElementById("p1");
+var d2 = document.getElementById("d2");
 
 function runTests() {
-  var zbox = document.getElementById("zbox");
-  var sbox = document.getElementById("sbox");
-  var p1 = document.getElementById("p1");
-  var d2 = document.getElementById("d2");
 
   checkClipRegion("p1", [[0, 0, 200, 100]]);
   checkClipRegion("p2", [[0, 0, 200, 50], [0, 50, 50, 150], [150, 50, 200, 150], [0, 150, 200, 200]]);
@@ -47,15 +47,30 @@ function runTests() {
   checkClipRegion("p2", [[0, 0, 200, 50], [0, 50, 50, 200], [150, 50, 200, 200]]);
 
   zbox.style.zIndex = -1;
-  flush();
+
+  // A non-zero timeout is needed on X11 (unless an XSync could be performed)
+  // to delay an OOP plugin's X requests enough so that the X server processes
+  // them after the parent processes requests (for the changes above).
+  setTimeout(part2, 1000);
+}
+
+function part2() {
   checkClipRegion("p2", [[0, 0, 200, 100], [0, 100, 50, 200], [150, 100, 200, 200]]);
 
   sbox.style.background = "";
-  flush();
+
+  setTimeout(part3, 1000);
+}
+
+function part3() {
   checkClipRegion("p2", [[0, 0, 200, 200]]);
   
   p1.style.zIndex = 1;
-  flush();
+
+  setTimeout(part4, 1000);
+}
+
+function part4() {
   checkClipRegion("p1", [[0, 0, 200, 200]]);
   checkClipRegion("p2", [[0, 100, 200, 200]]);
 
@@ -64,18 +79,17 @@ function runTests() {
   zbox.style.zIndex = 1;
   zbox.style.top = "50.3px;"
   d2.style.top = "100.3px";
-  flush();
-  checkClipRegionNoBounds("p2", [[0, 0, 200, 50], [0, 50, 50, 150], [150, 50, 200, 150], [0, 150, 200, 200]]);
+
+  setTimeout(done, 1000);
 }
 
-function flush() {
-  // This function is for X11 to flush the Xlib request queue.  It takes
-  // advantage of the current scrolling implementation, which will do this for
-  // us.  Beware though, it does not wait for the X server to process the
-  // events.
-  ++scroll.scrollTop;
-  --scroll.scrollTop;
+function done() {
+  checkClipRegionNoBounds("p2", [[0, 0, 200, 50], [0, 50, 50, 150], [150, 50, 200, 150], [0, 150, 200, 200]]);
+
+  window.opener.SimpleTest.finish();
+  window.close();
 }
+
 ]]>
 </script>
 
diff --git a/layout/generic/test/plugin_clipping_helper_table.xhtml b/layout/generic/test/plugin_clipping_helper_table.xhtml
index 58b046ec1da..bd4073e107a 100644
--- a/layout/generic/test/plugin_clipping_helper_table.xhtml
+++ b/layout/generic/test/plugin_clipping_helper_table.xhtml
@@ -2,8 +2,6 @@
 <?xml-stylesheet href="/tests/SimpleTest/test.css" type="text/css"?>
 <html xmlns="http://www.w3.org/1999/xhtml" title="Test Plugin Clipping: Plugins and Tables">
 <head>
-  <script type="application/javascript" src="/MochiKit/packed.js"></script>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
   <style>
   embed { width:300px; height:200px; display:block; }
   </style>
@@ -34,6 +32,9 @@ function runTests() {
   checkClipRegion("p1", [[0, 0, 300, 100]]);
   // p2 is partially covered by a table with an opaque background
   checkClipRegion("p2", [[0, 0, 300, 100]]);
+
+  window.opener.SimpleTest.finish();
+  window.close();
 }
 
 ]]>
diff --git a/layout/generic/test/plugin_clipping_helper_transformed.xhtml b/layout/generic/test/plugin_clipping_helper_transformed.xhtml
index 5a82f900aee..f18d159f75f 100644
--- a/layout/generic/test/plugin_clipping_helper_transformed.xhtml
+++ b/layout/generic/test/plugin_clipping_helper_transformed.xhtml
@@ -2,8 +2,6 @@
 <?xml-stylesheet href="/tests/SimpleTest/test.css" type="text/css"?>
 <html xmlns="http://www.w3.org/1999/xhtml" title="Test Plugin Clipping: Plugins in Transforms">
 <head>
-  <script type="application/javascript" src="/MochiKit/packed.js"></script>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
   <style>
   embed { width:300px; height:200px; display:block; }
   </style>
@@ -33,6 +31,9 @@ function runTests() {
   // p1 and p2 are both in a transformed context so they should be hidden.
   checkClipRegionNoBounds("p1", []);
   checkClipRegionNoBounds("p2", []);
+
+  window.opener.SimpleTest.finish();
+  window.close();
 }
 
 ]]>
diff --git a/layout/generic/test/plugin_clipping_lib.js b/layout/generic/test/plugin_clipping_lib.js
index d402ed03efe..39b8777f929 100644
--- a/layout/generic/test/plugin_clipping_lib.js
+++ b/layout/generic/test/plugin_clipping_lib.js
@@ -153,9 +153,6 @@ function loaded() {
 
   // Run actual test code
   runTests();
-
-  finish();
-  window.close();
 }
 
 // Need to run 'loaded' after painting is unsuppressed, or we'll set clip
