--- a/browser/components/sessionstore/src/SessionStore.jsm
+++ b/browser/components/sessionstore/src/SessionStore.jsm
@@ -370,24 +370,29 @@ let SessionStoreInternal = {
     if (this._initialized) {
       throw new Error("SessionStore.init() must only be called once!");
     }
 
     if (!aWindow) {
       throw new Error("SessionStore.init() must be called with a valid window.");
     }
 
+    this._disabledForMultiProcess = Services.prefs.getBoolPref("browser.tabs.remote");
+    if (this._disabledForMultiProcess) {
+      this._deferredInitialized.resolve();
+      return;
+    }
+
     TelemetryTimestamps.add("sessionRestoreInitialized");
     OBSERVING.forEach(function(aTopic) {
       Services.obs.addObserver(this, aTopic, true);
     }, this);
 
     this._initPrefs();
     this._initialized = true;
-    this._disabledForMultiProcess = this._prefBranch.getBoolPref("tabs.remote");
 
     // this pref is only read at startup, so no need to observe it
     this._sessionhistory_max_entries =
       this._prefBranch.getIntPref("sessionhistory.max_entries");
 
     // Wait until nsISessionStartup has finished reading the session data.
     gSessionStartup.onceInitialized.then(() => {
       // Parse session data and start restoring.
@@ -562,19 +567,16 @@ let SessionStoreInternal = {
     // Make sure to cancel pending saves.
     SessionSaver.cancel();
   },
 
   /**
    * Handle notifications
    */
   observe: function ssi_observe(aSubject, aTopic, aData) {
-    if (this._disabledForMultiProcess)
-      return;
-
     switch (aTopic) {
       case "domwindowopened": // catch new windows
         this.onOpen(aSubject);
         break;
       case "domwindowclosed": // catch closed windows
         this.onClose(aSubject);
         break;
       case "quit-application-requested":
@@ -1482,25 +1484,31 @@ let SessionStoreInternal = {
 
     this.restoreHistoryPrecursor(aWindow, [newTab], [tabState], 0, 0, 0,
                                  true /* Load this tab right away. */);
 
     return newTab;
   },
 
   setNumberOfTabsClosedLast: function ssi_setNumberOfTabsClosedLast(aWindow, aNumber) {
+    if (this._disabledForMultiProcess)
+      return;
+
     if ("__SSi" in aWindow) {
       return NumberOfTabsClosedLastPerWindow.set(aWindow, aNumber);
     }
 
     throw (Components.returnCode = Cr.NS_ERROR_INVALID_ARG);
   },
 
   /* Used to undo batch tab-close operations. Defaults to 1. */
   getNumberOfTabsClosedLast: function ssi_getNumberOfTabsClosedLast(aWindow) {
+    if (this._disabledForMultiProcess)
+      return 0;
+
     if ("__SSi" in aWindow) {
       // Blank tabs cannot be undo-closed, so the number returned by
       // the NumberOfTabsClosedLastPerWindow can be greater than the
       // return value of getClosedTabCount. We won't restore blank
       // tabs, so we return the minimum of these two values.
       return Math.min(NumberOfTabsClosedLastPerWindow.get(aWindow) || 1,
                       this.getClosedTabCount(aWindow));
     }