This patch has been ported to 3.6.4, may not be entirely correct.

Original patch was from bmo 460917, att 350845

---
--- browser/base/content/browser.js
+++ browser/base/content/browser.js
@@ -6009,9 +6009,18 @@
     var pluginInfo = getPluginInfo(aEvent.target);
     missingPluginsArray[pluginInfo.mimetype] = pluginInfo;
 
+ 
+    gBrowser.selectedBrowser.addEventListener("NewPluginInstalled",
+                                              gMissingPluginInstaller.refreshBrowser,
+                                              false);
+ 
     openDialog("chrome://mozapps/content/plugins/pluginInstallerWizard.xul",
                "PFSWindow", "chrome,centerscreen,resizable=yes",
                {plugins: missingPluginsArray, browser: gBrowser.selectedBrowser});
+
+    gBrowser.selectedBrowser.removeEventListener("NewPluginInstalled",
+                                                 gMissingPluginInstaller.refreshBrowser,
+                                                 false);
   },
 
   // Callback for user clicking on a disabled plugin
@@ -6107,11 +6116,19 @@
     function showPluginsMissing() {
       // get the urls of missing plugins
       var missingPluginsArray = gBrowser.selectedBrowser.missingPlugins;
+ 
+    gBrowser.selectedBrowser.addEventListener("NewPluginInstalled",
+                                              gMissingPluginInstaller.refreshBrowser,
+                                              false);
+ 
       if (missingPluginsArray) {
         window.openDialog("chrome://mozapps/content/plugins/pluginInstallerWizard.xul",
                           "PFSWindow", "chrome,centerscreen,resizable=yes",
                           {plugins: missingPluginsArray, browser: gBrowser.selectedBrowser});
       }
+    gBrowser.selectedBrowser.removeEventListener("NewPluginInstalled",
+                                                 gMissingPluginInstaller.refreshBrowser,
+                                                 false);
     }
 
     if (aEvent.type == "PluginBlocklisted") {
@@ -6442,6 +6459,13 @@
       notificationBox.removeNotification(notification);
     }
     // reload the browser to make the new plugin show.
+  
+    // reload plugins
+    var pm = Components.classes["@mozilla.org/plugin/manager;1"]
+                 .getService(Components.interfaces.nsIPluginManager);
+    pm.reloadPlugins(false);
+  
+    // ... and reload the browser to activate new plugins available
     browser.reload();
   }
 };