Microsoft’s MSN and Bing departments have a history of getting cozy with Mozilla’s web browser. Today, there came a proud announcement that msnNOW is available as a Firefox sidebar.In the past, releases have taken two basic forms. First, there’s the fully-customized Firefox browser — an idea that Ron Burgundy would no doubt find mind-bottling. Second, there’s the customization extension. That allows existing Firefox users to instantly add all the MSN/Bing goodies to their browsers instead of replacing it with the weird Microsoft/Mozilla Frankenbrowser.The new msnNOW add-on is actually a Firefox sidebar. That’s pretty cutting edge stuff, considering that it’s only available in the non-stable Firefox builds right now. MSN is also in pretty select company here. About the only other big-name adopter of the sidebar you’re likely to have heard about is Microsoft’s social networking pal Facebook.Activating the bar is simple enough: just head to this page and turn it on. As soon as you do, you’ll see a stream of trending topics from Facebook, Twitter, and Bing appear on the right edge of your Firefox window. As with the Facebook bar, you can also click the chat bubble icon on the Firefox toolbar to change settings for desktop notifications or to disable the extension completely.As bizarre as it seems for a Microsoft division to be showing some love for a competitor’s browser, there’s certainly a good reason to do it. Firefox has hundreds of millions of users, and that means there’s an opportunity to get MSN and Bing additional face time with folks while they browse.Who knows, one silly cat picture and a convincing banner ad for IE later and Microsoft could pick up a thousand converts. The odds aren’t in Microsoft’s favor, but unlikely things do happen all the time on the Internet.