diff --git a/toolkit/content/widgets/browser.xml b/toolkit/content/widgets/browser.xml
index c30f626250ec..90b8a259fca1 100644
--- a/toolkit/content/widgets/browser.xml
+++ b/toolkit/content/widgets/browser.xml
@@ -844,7 +844,7 @@
             if (this.docShell && this.webNavigation.sessionHistory) {
               var os = Components.classes["@mozilla.org/observer-service;1"]
                                  .getService(Components.interfaces.nsIObserverService);
-              os.addObserver(this, "browser:purge-session-history", false);
+              os.addObserver(this, "browser:purge-session-history", true);
 
               // enable global history if we weren't told otherwise
               if (!this.hasAttribute("disableglobalhistory") && !this.isRemoteBrowser) {
diff --git a/toolkit/content/widgets/remote-browser.xml b/toolkit/content/widgets/remote-browser.xml
index 9c74bfce504c..60bd45b1de4d 100644
--- a/toolkit/content/widgets/remote-browser.xml
+++ b/toolkit/content/widgets/remote-browser.xml
@@ -364,7 +364,7 @@
           }
 
           if (!this.hasAttribute("disablehistory")) {
-            Services.obs.addObserver(this, "browser:purge-session-history", false)
+            Services.obs.addObserver(this, "browser:purge-session-history", true)
           }
 
           let jsm = "resource://gre/modules/RemoteController.jsm";