diff --git a/mozilla/xpfe/appshell/src/nsXULWindow.cpp b/mozilla/xpfe/appshell/src/nsXULWindow.cpp
index d9f7ccb8be3..784a56d658b 100644
--- a/mozilla/xpfe/appshell/src/nsXULWindow.cpp
+++ b/mozilla/xpfe/appshell/src/nsXULWindow.cpp
@@ -1632,8 +1632,23 @@ nsresult nsXULWindow::ContentShellAdded(nsIDocShellTreeItem* aContentShell,
     }
 #endif
     
-    NS_ENSURE_TRUE(mTargetableShells.AppendObject(contentShellWeak),
-                   NS_ERROR_OUT_OF_MEMORY);
+    // put the new shell at the start of the targetable shells list if either
+    // it's the new primary shell or there is no existing primary shell (which
+    // means that chances are this one just stopped being primary).  If we
+    // really cared, we could keep track of the "last no longer primary shell"
+    // explicitly, but it probably doesn't matter enough: the difference would
+    // only be felt in a situation where all shells were non-primary, which
+    // doesn't happen much.  In a situation where there is one and only one
+    // primary shell, and in which shells get unmarked as primary before some
+    // other shell gets marked as primary, this effectively stores the list of
+    // targetable shells in "most recently primary first" order.
+    PRBool inserted;
+    if (aPrimary || !mPrimaryContentShell) {
+      inserted = mTargetableShells.InsertObjectAt(contentShellWeak, 0);
+    } else {
+      inserted = mTargetableShells.AppendObject(contentShellWeak);
+    }
+    NS_ENSURE_TRUE(inserted, NS_ERROR_OUT_OF_MEMORY);
   }
 
   return NS_OK;