Send to Kindle for Firefox works pretty much the same as the Chrome plugin. After you've installed the plugin, navigate to the page which you wish to save and click the Kindle icon on your browser's menu bar. The plugin will strip out the advertising and other dross and let you send just the article to your Kindle.
Amazon has also released apps for Windows and OSX which offer similar features, and the latest version of Kindle for Android includes a similar menu option which will let you send files to your Kindle - on some versions of Android, at least.
Clever move, this. By offering you more and more ways to move your content onto the Kindle platform Amazon is giving readers more and more reasons to stay inside the Kindle ecosystem, where Amazon will have more opportunities to pitch more content.