Meebo, for those who don't know it yet, is a web-based IM solution that enables you to log on to different IM services simultaneously and chat with all your buddies from a single interface, no matter which network they belong to.
Now Meebo has launched this add-on that builds the web application right into Firefox.
You don't need to register a Meebo account in order to use this add-on but, if you do, you'll be able to see all your contacts across multiple networks in the browser's sidebar (otherwise you would only see a single IM list).
This Meebo add-on serves a good functional purpose, but it still needs some polishing. For example, you can't login to two or more simultaneous networks from the sidebar (you need to visit Meebo's homepage to do so) and you must have the Meebo tab permanently open, to name just two of the most annoying issues.
Despite its flaws, Meebo for Firefox can be especially useful for Meebo users, as it seamlessly integrates this IM platform into your favorite web browser.