Firefox extensions (a.k.a. add-ons) get updated from time to time. As you may know, you can check for updates yourself by clicking Tools, Add-ons, Updates, or just wait for the browser to notify you (which it does automatically from time to time).
Ah, but what about Plugins, which make it possible to open PDFs right in your browser, view Adobe Flash and Microsoft Silverlight videos, update your Google applications, and the like? Firefox doesn't do automatic update checks for Plugins (yet--one must assume that's in the works), but thanks to a new Mozilla site, you can run a check yourself.
It's called, aptly enough, Plugin Check, and using it is as simple as visiting the site. In just a few seconds you'll see the results for all your Plugins. Hopefully they're all green, meaning "up to date," but you may see some that are yellow, meaning an update is required.
No worries: Just click the corresponding Update button to download and install it.
If the checker can't determine a particular Plugin's status, you'll get a gray Research button you can click to run a Google search. That's not particularly handy, but at least you can find your way to the Plugin creator's Web site.
I'd recommend visiting Plugin Check once a month or so, just to make sure you're not running any outdated Plugins.