Firefox is still my default web browser, love it or hate but I love it. Most of general users know about Firefox add-ons but Firefox has some plugins too. It is recommended to update your plugins for security reason and to run Firefox smoothly. See above screen shot QuickTime plugin is not updated and showing Vulnerable so easily can attack on our browser. Silverlight plugin is also out of dated.
Firefox has a page PluginCheck there you can go check for plugin updates. You can check for plugin updates by going to tools menu and opening Add-ons.
Go for PluginCheck.