--- a/content/xul/document/src/nsXULPrototypeCache.cpp
+++ b/content/xul/document/src/nsXULPrototypeCache.cpp
@@ -140,16 +140,17 @@ NS_NewXULPrototypeCache(nsISupports* aOu
     nsresult rv = result->QueryInterface(aIID, aResult);
 
     nsCOMPtr<nsIObserverService> obsSvc =
         mozilla::services::GetObserverService();
     if (obsSvc && NS_SUCCEEDED(rv)) {
         nsXULPrototypeCache *p = result;
         obsSvc->AddObserver(p, "chrome-flush-skin-caches", PR_FALSE);
         obsSvc->AddObserver(p, "chrome-flush-caches", PR_FALSE);
+        obsSvc->AddObserver(p, "startupcache-invalidate", PR_FALSE);
     }
 
     return rv;
 }
 
 /* static */ nsXULPrototypeCache*
 nsXULPrototypeCache::GetInstance()
 {
@@ -405,50 +406,59 @@ static PRBool gChecksumXULFastLoadFile =
 
 void
 nsXULPrototypeCache::AbortFastLoads()
 {
 #ifdef DEBUG_brendan
     NS_BREAK();
 #endif
 
-    // Save a strong ref to the FastLoad file, so we can remove it after we
-    // close open streams to it.
-    nsCOMPtr<nsIFile> file = gFastLoadFile;
-
     // Flush the XUL cache for good measure, in case we cached a bogus/downrev
     // script, somehow.
     Flush();
 
     // Clear the FastLoad set
     mFastLoadURITable.Clear();
 
-    if (! gFastLoadService)
-        return;
+    nsCOMPtr<nsIFastLoadService> fastLoadService = gFastLoadService;
+    nsCOMPtr<nsIFile> file = gFastLoadFile;
+
+    nsresult rv;
+
+    if (! fastLoadService) {
+        fastLoadService = do_GetFastLoadService();
+        if (! fastLoadService)
+            return;
+
+        rv = fastLoadService->NewFastLoadFile(XUL_FASTLOAD_FILE_BASENAME,
+                                              getter_AddRefs(file));
+        if (NS_FAILED(rv))
+            return;
+    }
 
     // Fetch the current input (if FastLoad file existed) or output (if we're
     // creating the FastLoad file during this app startup) stream.
     nsCOMPtr<nsIObjectInputStream> objectInput;
     nsCOMPtr<nsIObjectOutputStream> objectOutput;
-    gFastLoadService->GetInputStream(getter_AddRefs(objectInput));
-    gFastLoadService->GetOutputStream(getter_AddRefs(objectOutput));
+    fastLoadService->GetInputStream(getter_AddRefs(objectInput));
+    fastLoadService->GetOutputStream(getter_AddRefs(objectOutput));
 
     if (objectOutput) {
-        gFastLoadService->SetOutputStream(nsnull);
+        fastLoadService->SetOutputStream(nsnull);
 
         if (NS_SUCCEEDED(objectOutput->Close()) && gChecksumXULFastLoadFile)
-            gFastLoadService->CacheChecksum(gFastLoadFile,
-                                            objectOutput);
+            fastLoadService->CacheChecksum(file,
+                                           objectOutput);
     }
 
     if (objectInput) {
         // If this is the last of one or more XUL master documents loaded
         // together at app startup, close the FastLoad service's singleton
         // input stream now.
-        gFastLoadService->SetInputStream(nsnull);
+        fastLoadService->SetInputStream(nsnull);
         objectInput->Close();
     }
 
     // Now rename or remove the file.
     if (file) {
 #ifdef DEBUG
         // Remove any existing Aborted.mfasl files generated in previous runs.
         nsCOMPtr<nsIFile> existingAbortedFile;
@@ -457,23 +467,25 @@ nsXULPrototypeCache::AbortFastLoads()
             existingAbortedFile->SetLeafName(NS_LITERAL_STRING("Aborted.mfasl"));
             PRBool fileExists = PR_FALSE;
             existingAbortedFile->Exists(&fileExists);
             if (fileExists)
                 existingAbortedFile->Remove(PR_FALSE);
         }
         file->MoveToNative(nsnull, NS_LITERAL_CSTRING("Aborted.mfasl"));
 #else
-        file->Remove(PR_FALSE);
+        rv = file->Remove(PR_FALSE);
+        if (NS_FAILED(rv))
+            NS_WARNING("Failed to remove fastload file, fastload data may be outdated");
 #endif
     }
 
     // If the list is empty now, the FastLoad process is done.
-    NS_RELEASE(gFastLoadService);
-    NS_RELEASE(gFastLoadFile);
+    NS_IF_RELEASE(gFastLoadService);
+    NS_IF_RELEASE(gFastLoadFile);
 }
 
 
 void
 nsXULPrototypeCache::RemoveFromFastLoadSet(nsIURI* aURI)
 {
     mFastLoadURITable.Remove(aURI);
 }

--- a/toolkit/mozapps/extensions/test/xpcshell/test_bug594058.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_bug594058.js
@@ -7,56 +7,74 @@
 
 // Disables security checking our updates which haven't been signed
 Services.prefs.setBoolPref("extensions.checkUpdateSecurity", false);
 
 const Ci = Components.interfaces;
 const extDir = gProfD.clone();
 extDir.append("extensions");
 
+var gFastLoadService = AM_Cc["@mozilla.org/fast-load-service;1"].
+                       getService(AM_Ci.nsIFastLoadService);
+var gFastLoadFile = null;
+
 /**
  * Start the test by installing extensions.
  */
 function run_test() {
   do_test_pending();
   let cachePurged = false;
 
   let obs = AM_Cc["@mozilla.org/observer-service;1"].
     getService(AM_Ci.nsIObserverService);
   obs.addObserver({
     observe: function(aSubject, aTopic, aData) {
       cachePurged = true;
     }
   }, "startupcache-invalidate", false);
   createAppInfo("xpcshell@tests.mozilla.org", "XPCShell", "1", "1");
+
+  gFastLoadFile = gFastLoadService.newFastLoadFile("XUL");
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
+
   startupManager();
+  // nsAppRunner takes care of clearing this when a new app is installed
+  do_check_true(gFastLoadFile.exists());
 
   installAllFiles([do_get_addon("test_bug594058")], function() {
     restartManager();
+    do_check_false(gFastLoadFile.exists());
+    gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
     do_check_true(cachePurged);
     cachePurged = false;
 
     // Now, make it look like we've updated the file. First, start the EM
     // so it records the bogus old time, then update the file and restart.
     let extFile = extDir.clone();
     let pastTime = extFile.lastModifiedTime - 5000;
     extFile.append("bug594058@tests.mozilla.org");
     setExtensionModifiedTime(extFile, pastTime);
     let otherFile = extFile.clone();
     otherFile.append("directory");
     otherFile.lastModifiedTime = pastTime;
     otherFile.append("file1");
     otherFile.lastModifiedTime = pastTime;
 
     restartManager();
+    do_check_false(gFastLoadFile.exists());
+    gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
     cachePurged = false;
 
     otherFile.lastModifiedTime = pastTime + 5000;
     restartManager();
+    do_check_false(gFastLoadFile.exists());
+    gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
     do_check_true(cachePurged);
     cachePurged = false;
 
     restartManager();
-    do_check_true(!cachePurged);
+    do_check_true(gFastLoadFile.exists());
+    do_check_false(cachePurged);
 
     do_test_finished();
   });  
 }

--- a/toolkit/mozapps/extensions/test/xpcshell/test_startup.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/test_startup.js
@@ -80,21 +80,29 @@ globalDir.append(gAppInfo.ID);
 registerDirectory("XRESysSExtPD", globalDir.parent);
 const userDir = gProfD.clone();
 userDir.append("extensions3");
 userDir.append(gAppInfo.ID);
 registerDirectory("XREUSysExt", userDir.parent);
 const profileDir = gProfD.clone();
 profileDir.append("extensions");
 
+var gFastLoadService = AM_Cc["@mozilla.org/fast-load-service;1"].
+                       getService(AM_Ci.nsIFastLoadService);
+var gFastLoadFile = null;
+
 // Set up the profile
 function run_test() {
   do_test_pending();
   startupManager();
 
+  gFastLoadFile = gFastLoadService.newFastLoadFile("XUL");
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
+
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
     do_check_eq(a1, null);
@@ -122,16 +130,19 @@ function run_test_1() {
   // the change in run_test_2 makes the last modified time change.
   setExtensionModifiedTime(dest, dest.lastModifiedTime - 5000);
 
   writeInstallRDFForExtension(addon3, profileDir);
   writeInstallRDFForExtension(addon4, profileDir);
   writeInstallRDFForExtension(addon5, profileDir);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
+
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
     do_check_neq(a1, null);
@@ -198,16 +209,18 @@ function run_test_2() {
   writeInstallRDFForExtension(addon2, globalDir);
   addon2.version="2.3";
   writeInstallRDFForExtension(addon2, userDir);
   var dest = profileDir.clone();
   dest.append(do_get_expected_addon_name("addon3@tests.mozilla.org"));
   dest.remove(true);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -252,16 +265,18 @@ function run_test_3() {
   dest.append(do_get_expected_addon_name("addon1@tests.mozilla.org"));
   dest.remove(true);
   dest = profileDir.clone();
   dest.append(do_get_expected_addon_name("addon2@tests.mozilla.org"));
   dest.remove(true);
   writeInstallRDFForExtension(addon3, profileDir, "addon4@tests.mozilla.org");
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -303,16 +318,18 @@ function run_test_3() {
   });
 }
 
 // Test that disabling an install location works
 function run_test_4() {
   Services.prefs.setIntPref("extensions.enabledScopes", AddonManager.SCOPE_SYSTEM);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -335,16 +352,18 @@ function run_test_4() {
   });
 }
 
 // Switching disabled locations works
 function run_test_5() {
   Services.prefs.setIntPref("extensions.enabledScopes", AddonManager.SCOPE_USER);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -373,16 +392,18 @@ function run_test_5() {
   });
 }
 
 // Resetting the pref makes everything visible again
 function run_test_6() {
   Services.prefs.clearUserPref("extensions.enabledScopes");
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -415,16 +436,18 @@ function run_test_6() {
 function run_test_7() {
   addon1.version = "1.2";
   writeInstallRDFForExtension(addon1, profileDir);
   var dest = userDir.clone();
   dest.append(do_get_expected_addon_name("addon2@tests.mozilla.org"));
   dest.remove(true);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -462,16 +485,18 @@ function run_test_7() {
   });
 }
 
 // Disabling all locations still leaves the profile working
 function run_test_8() {
   Services.prefs.setIntPref("extensions.enabledScopes", 0);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -503,16 +528,18 @@ function run_test_9() {
   dest.remove(true);
   dest = globalDir.clone();
   dest.append(do_get_expected_addon_name("addon2@tests.mozilla.org"));
   dest.remove(true);
   addon2.version = "2.4";
   writeInstallRDFForExtension(addon2, profileDir);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -553,16 +580,18 @@ function run_test_9() {
 function run_test_10() {
   var dest = profileDir.clone();
   dest.append(do_get_expected_addon_name("addon1@tests.mozilla.org"));
   dest.remove(true);
   addon1.version = "1.3";
   writeInstallRDFForExtension(addon1, userDir);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {
 
@@ -603,16 +632,18 @@ function run_test_11() {
   var dest = userDir.clone();
   dest.append(do_get_expected_addon_name("addon1@tests.mozilla.org"));
   dest.remove(true);
   dest = profileDir.clone();
   dest.append(do_get_expected_addon_name("addon2@tests.mozilla.org"));
   dest.remove(true);
 
   restartManager();
+  do_check_false(gFastLoadFile.exists());
+  gFastLoadFile.create(AM_Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
 
   AddonManager.getAddonsByIDs(["addon1@tests.mozilla.org",
                                "addon2@tests.mozilla.org",
                                "addon3@tests.mozilla.org",
                                "addon4@tests.mozilla.org",
                                "addon5@tests.mozilla.org"],
                                function([a1, a2, a3, a4, a5]) {