Hootbar (formerly known as Twitterbar) is an extension for Mozilla Firefox that allows you to automatically post to Twitter the address of the webpage that you're viewing, so you can share your favorite sites with your contacts and the wider world.
Using it is very simple. Once installed, a small button will appear to the right of the address bar on your browser. Clicking it will post the current web address to your Twitter account.
Among the options available with the program, you can configure a predetermined account and modify the standard message that will be attached to these posts.
All of this makes Hootbar an extension that earns its spot on your browser.