1 Open a new tab and type about:config into the address bar. 2 Click
on the button that says "I'll be careful, I promise". 3 In the search bar at
the top, type plugins.load 4 That will show you a line which says
plugins.load_appdir_plugins - which will be set to false. 5 Highlight that
line by right-clicking on it. Select "Toggle" - that will change the setting to
true. 6 Close the tab and restart Firefox. Your missing plugin(s) should now
be visible and work as before.