--- a/toolkit/mozapps/update/tests/chrome/test_0083_error_patchApplyFailure_partial_complete.xul
+++ b/toolkit/mozapps/update/tests/chrome/test_0083_error_patchApplyFailure_partial_complete.xul
@@ -18,25 +18,29 @@
 
 <script type="application/javascript">
 <![CDATA[
 
 const TESTS = [ {
   pageid: PAGEID_ERROR_PATCHING,
   buttonClick: "next"
 }, {
-  pageid: PAGEID_DOWNLOADING
+  pageid: PAGEID_DOWNLOADING,
+  extraStartFunction: createContinueFile
 }, {
   pageid: PAGEID_FINISHED,
-  buttonClick: "extra1"
+  buttonClick: "extra1",
+  extraStartFunction: removeContinueFile
 } ];
 
 function runTest() {
   debugDump("entering");
 
+  removeContinueFile();
+
   // Specify the url to update.sjs with a slowDownloadMar param so the ui can
   // load before the download completes.
   let slowDownloadURL = URL_HTTP_UPDATE_XML + "?slowDownloadMar=1";
   let patches = getLocalPatchString("partial", null, null, null, null, null,
                                     STATE_PENDING) +
                 getLocalPatchString("complete", slowDownloadURL, null, null,
                                     null, "false");
   let updates = getLocalUpdateString(patches, null, null, null,

--- a/toolkit/mozapps/update/tests/chrome/test_0084_error_patchApplyFailure_verify_failed.xul
+++ b/toolkit/mozapps/update/tests/chrome/test_0084_error_patchApplyFailure_verify_failed.xul
@@ -11,32 +11,37 @@
 <window title="Update Wizard pages: error patching, download, and errors (partial failed and download complete verification failure)"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
         onload="runTestDefault();">
 <script type="application/javascript"
         src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
 <script type="application/javascript"
         src="utils.js"/>
 
+<script type="application/javascript" src="chrome://mochikit/content/chrome-harness.js"></script>
 <script type="application/javascript">
 <![CDATA[
 
 const TESTS = [ {
   pageid: PAGEID_ERROR_PATCHING,
   buttonClick: "next"
 }, {
-  pageid: PAGEID_DOWNLOADING
+  pageid: PAGEID_DOWNLOADING,
+  extraStartFunction: createContinueFile
 }, {
   pageid: PAGEID_ERRORS,
-  buttonClick: "finish"
+  buttonClick: "finish",
+  extraStartFunction: removeContinueFile
 } ];
 
 function runTest() {
   debugDump("entering");
 
+  removeContinueFile();
+
   // Specify the url to update.sjs with a slowDownloadMar param so the ui can
   // load before the download completes.
   let slowDownloadURL = URL_HTTP_UPDATE_XML + "?slowDownloadMar=1";
   let patches = getLocalPatchString("partial", null, null, null, null, null,
                                     STATE_PENDING) +
                 getLocalPatchString("complete", slowDownloadURL, "MD5",
                                     "1234cd43a1c77e30191c53a329a3f99d", null,
                                     "false");

--- a/toolkit/mozapps/update/tests/chrome/update.sjs
+++ b/toolkit/mozapps/update/tests/chrome/update.sjs
@@ -39,33 +39,47 @@ function handleRequest(aRequest, aRespon
   }
 
   // When a mar download is started by the update service it can finish
   // downloading before the ui has loaded. By specifying a serviceURL for the
   // update patch that points to this file and has a slowDownloadMar param the
   // mar will be downloaded asynchronously which will allow the ui to load
   // before the download completes.
   if (params.slowDownloadMar) {
+    var i;
     aResponse.processAsync();
     aResponse.setHeader("Content-Type", "binary/octet-stream");
     aResponse.setHeader("Content-Length", SIZE_SIMPLE_MAR);
+    var continueFile = AUS_Cc["@mozilla.org/file/directory_service;1"].
+                       getService(AUS_Ci.nsIProperties).
+                       get("CurWorkD", AUS_Ci.nsILocalFile);
+    var continuePath = REL_PATH_DATA + "continue";
+    var continuePathParts = continuePath.split("/");
+    for (i = 0; i < continuePathParts.length; ++i) {
+      continueFile.append(continuePathParts[i]);
+    }
+
     var marFile = AUS_Cc["@mozilla.org/file/directory_service;1"].
                   getService(AUS_Ci.nsIProperties).
                   get("CurWorkD", AUS_Ci.nsILocalFile);
     var path = REL_PATH_DATA + FILE_SIMPLE_MAR;
     var pathParts = path.split("/");
-    for(var i = 0; i < pathParts.length; ++i)
+    for (i = 0; i < pathParts.length; ++i) {
       marFile.append(pathParts[i]);
+    }
     var contents = readFileBytes(marFile);
     gTimer = AUS_Cc["@mozilla.org/timer;1"].
              createInstance(AUS_Ci.nsITimer);
     gTimer.initWithCallback(function(aTimer) {
-      aResponse.write(contents);
-      aResponse.finish();
-    }, SLOW_MAR_DOWNLOAD_INTERVAL, AUS_Ci.nsITimer.TYPE_ONE_SHOT);
+      if (continueFile.exists()) {
+        gTimer.cancel();
+        aResponse.write(contents);
+        aResponse.finish();
+      }
+    }, SLOW_MAR_DOWNLOAD_INTERVAL, AUS_Ci.nsITimer.TYPE_REPEATING_SLACK);
     return;
   }
 
   if (params.uiURL) {
     var remoteType = "";
     if (!params.remoteNoTypeAttr &&
         (params.uiURL == "BILLBOARD" || params.uiURL == "LICENSE")) {
       remoteType = " " + params.uiURL.toLowerCase() + "=\"1\"";

--- a/toolkit/mozapps/update/tests/chrome/utils.js
+++ b/toolkit/mozapps/update/tests/chrome/utils.js
@@ -478,29 +478,68 @@ function delayedDefaultCallback() {
     gTest.extraDelayedCheckFunction();
   }
 
   // Used to verify that this test has been performed
   gTest.ranTest = true;
 
   if (gTest.buttonClick) {
     debugDump("clicking " + gTest.buttonClick + " button");
-    if(gTest.extraDelayedFinishFunction) {
+    if (gTest.extraDelayedFinishFunction) {
       throw("Tests cannot have a buttonClick and an extraDelayedFinishFunction property");
     }
     gDocElem.getButton(gTest.buttonClick).click();
   }
   else if (gTest.extraDelayedFinishFunction) {
     debugDump("calling extraDelayedFinishFunction " +
               gTest.extraDelayedFinishFunction.name);
     gTest.extraDelayedFinishFunction();
   }
 }
 
 /**
+ * Gets the continue file used to signal the mock http server to continue
+ * downloading for slow download mar file tests without creating it.
+ *
+ * @return nsILocalFile for the continue file.
+ */
+function getContinueFile() {
+  let continueFile = AUS_Cc["@mozilla.org/file/directory_service;1"].
+                     getService(AUS_Ci.nsIProperties).
+                     get("CurWorkD", AUS_Ci.nsILocalFile);
+  let continuePath = REL_PATH_DATA + "/continue";
+  let continuePathParts = continuePath.split("/");
+  for (let i = 0; i < continuePathParts.length; ++i) {
+    continueFile.append(continuePathParts[i]);
+  }
+  return continueFile;
+}
+
+/**
+ * Creates the continue file used to signal the mock http server to continue
+ * downloading for slow download mar file tests.
+ */
+function createContinueFile() {
+  debugDump("creating 'continue' file for slow mar downloads");
+  writeFile(getContinueFile(), "");
+}
+
+/**
+ * Removes the continue file used to signal the mock http server to continue
+ * downloading for slow download mar file tests.
+ */
+function removeContinueFile() {
+  let continueFile = getContinueFile();
+  if (continueFile.exists()) {
+    debugDump("removing 'continue' file for slow mar downloads");
+    continueFile.remove(false);
+  }
+}
+
+/**
  * Checks the wizard page buttons' disabled and hidden attributes values are
  * correct. If an expected button id is not specified then the expected disabled
  * and hidden attribute value is true.
  */
 function checkButtonStates() {
   debugDump("entering - TESTS[" + gTestCounter + "], pageid: " + gTest.pageid);
 
   const buttonNames = ["extra1", "extra2", "back", "next", "finish", "cancel"];