diff --git a/toolkit/mozapps/extensions/src/nsExtensionManager.js.in b/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
index 3ac329e85ebe..5ad7995401b3 100644
--- a/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
+++ b/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
@@ -176,6 +176,7 @@ var gOSTarget             = null;
 var gConsole              = null;
 var gInstallManifestRoot  = null;
 var gVersionChecker       = null;
+var gDirService           = null;
 var gLoggingEnabled       = null;
 var gCheckCompatibility   = true;
 var gCheckUpdateSecurity  = true;
@@ -367,9 +368,12 @@ function getDirNoCreate(key, pathArray) {
  * @return  nsIFile object for the location specified.
  */
 function getDirInternal(key, pathArray, shouldCreate) {
-  var fileLocator = Cc["@mozilla.org/file/directory_service;1"].
-                    getService(Ci.nsIProperties);
-  var dir = fileLocator.get(key, Ci.nsILocalFile);
+  if (!gDirService) {
+    gDirService = Cc["@mozilla.org/file/directory_service;1"].
+                  getService(Ci.nsIProperties);
+  }
+
+  var dir = gDirService.get(key, Ci.nsILocalFile);
   for (var i = 0; i < pathArray.length; ++i) {
     dir.append(pathArray[i]);
     if (shouldCreate && !dir.exists())
@@ -2695,6 +2699,7 @@ ExtensionManager.prototype = {
     gPref = null;
     gConsole = null;
     gVersionChecker = null;
+    gDirService = null;
     gInstallManifestRoot = null;
     gApp = null;
   },
@@ -2707,16 +2712,20 @@ ExtensionManager.prototype = {
    *          be rebuilt, false otherwise.
    */
   _ensureDatasetIntegrity: function EM__ensureDatasetIntegrity() {
-    var extensionsDS = getFile(KEY_PROFILEDIR, [FILE_EXTENSIONS]);
-    var extensionsINI = getFile(KEY_PROFILEDIR, [FILE_EXTENSION_MANIFEST]);
-    var extensionsCache = getFile(KEY_PROFILEDIR, [FILE_EXTENSIONS_STARTUP_CACHE]);
+    var profD = getDirNoCreate(KEY_PROFILEDIR, []);
+    var extensionsDS = profD.clone();
+    extensionsDS.append(FILE_EXTENSIONS);
+    var extensionsINI = profD.clone();
+    extensionsINI.append(FILE_EXTENSION_MANIFEST);
+    var extensionsCache = profD;
+    extensionsCache.append(FILE_EXTENSIONS_STARTUP_CACHE);
 
     var dsExists = extensionsDS.exists();
     var iniExists = extensionsINI.exists();
     var cacheExists = extensionsCache.exists();
 
     if (dsExists && iniExists && cacheExists)
-      return false;
+      return [false, !iniExists];
 
     // If any of the files are missing, remove the .ini file
     if (iniExists)
@@ -2726,29 +2735,20 @@ ExtensionManager.prototype = {
     if (!dsExists && cacheExists)
       extensionsCache.remove(false);
 
-    return true;
+    return [true, !iniExists];
   },
 
   /**
    * See nsIExtensionManager.idl
    */
   start: function EM_start(commandLine) {
-    var isDirty = false;
-    var forceAutoReg = false;
-
-    // Somehow the component list went away, and for that reason the new one
-    // generated by this function is going to result in a different compreg.
-    // We must force a restart.
-    var componentList = getFile(KEY_PROFILEDIR, [FILE_EXTENSION_MANIFEST]);
-    if (!componentList.exists())
-      forceAutoReg = true;
+    var isDirty, forceAutoReg;
 
     // Check for missing manifests - e.g. missing extensions.ini, missing
     // extensions.cache, extensions.rdf etc. If any of these files
     // is missing then we are in some kind of weird or initial state and need
     // to force a regeneration.
-    if (this._ensureDatasetIntegrity())
-      isDirty = true;
+    [isDirty, forceAutoReg] = this._ensureDatasetIntegrity();
 
     // Block attempts to flush for the entire startup
     gAllowFlush = false;
@@ -3615,9 +3615,8 @@ ExtensionManager.prototype = {
     gAllowFlush = false;
 
     // Make the extensions datasource consistent if it isn't already.
-    var isDirty = false;
-    if (this._ensureDatasetIntegrity())
-      isDirty = true;
+    var isDirty;
+    [isDirty,] = this._ensureDatasetIntegrity();
 
     if (this._checkForFileChanges())
       isDirty = true;