Recently, Mozilla announced that they plan to gradually eliminate plugins from Firefox.
Plugins are used in Firefox to allow certain types of content to be embedded in a web page. Common plugins are those for Flash, Adobe Reader (PDFs), Java, Silverlight and Shockwave. According to Mozilla, plugins are often a source of performance and security issues, and they are being made increasingly redundant, given new technologies like HTML5.
It’s important to distinguish between Firefox plugins and Firefox extensions. Extensions provide new functionality to the browser, and include SEO tools, debugging tools, media helpers, interface customizations, and so on. Mozilla has no plans to phase out extensions, only plugins. A post over at ColonelPanic provides additional information about the distinction between plugins and extensions.
For now, the main thing you need to know about plugins in Firefox is that they can now be configured to remain inactive until explicitly activated by the user. I’ve changed all my Firefox plugins to ‘Ask to activate’ and so far it’s working well. It means there’s an extra step whenever I want to display embedded content, but it also means that content doesn’t do anything automatically, and I always know exactly what’s generating that content (Java, Flash, etc.) I highly recommend doing this. From the Firefox menu, select ‘Add-ons’ to configure your plugins.