--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -5150,24 +5150,24 @@ var TabsProgressListener = {
           return;
         aBrowser.removeEventListener("pagehide", onPageHide, true);
         if (event.target.documentElement)
           event.target.documentElement.removeAttribute("hasBrowserHandlers");
       }, true);
     }
   },
 
-  onLocationChange(aBrowser, aWebProgress, aRequest, aLocationURI,
-                             aFlags) {
+  onLocationChange(aBrowser, aWebProgress, aRequest, aLocationURI, aFlags) {
     // Filter out location changes caused by anchor navigation
     // or history.push/pop/replaceState.
     if (aFlags & Ci.nsIWebProgressListener.LOCATION_CHANGE_SAME_DOCUMENT) {
-      // Reader mode actually cares about these:
-      let mm = gBrowser.selectedBrowser.messageManager;
-      mm.sendAsyncMessage("Reader:PushState", {isArticle: gBrowser.selectedBrowser.isArticle});
+      // Reader mode cares about history.pushState and friends.
+      aBrowser.messageManager.sendAsyncMessage("Reader:PushState", {
+        isArticle: aBrowser.isArticle,
+      });
       return;
     }
 
     // Filter out location changes in sub documents.
     if (!aWebProgress.isTopLevel)
       return;
 
     // Only need to call locationChange if the PopupNotifications object