Sometimes when you visit a website you’ll see an “Additional plugins are required to display…” notification at the top of Firefox. Usually it is because you legitimately don’t have the correct plugin to view content on the website (such as Flash player) but other times it may be because the website wants you to install something malicious. If you’ve chosen not to install Flash or other plugins, you’ll see the “missing plugin” notification all of the time. So, lets fix that and get rid of the notification.
Type about:config into the Firefox address bar.
On the humorous “void your warranty” page, Click I’ll be careful, I promise!.
In the filter box, Type missing_plugin.
Now in the preference list below, Right-Click plugins.hide_infobar_for_missing_plugin and Select Toggle.
Now when you visit a website with a plugin you don’t have installed, Firefox will no longer prompt you with the annoying “missing plugin” bar at the top of it. On my computer setup I don’t have Flash installed, so this fix comes in handy when viewing websites that have flash-based advertisements and pop-outs.