Firefox with MSN is a customized version of Firefox for MSN users. Firefox with MSN sets Bing as the default search engine in the search box and AwesomeBar, saves msnNOW in a convenient Firefox App Tab and makes MSN.com your default home page. It also gives your Firefox an MSN theme and provides quick access links to popular MSN channels so you can easily get real time updates for news, entertainment, sports and the things that matter most to you.
You can get Firefox with MSN here. Existing Firefox users can get the custom experience by downloading the Firefox with MSN add-on.
News source: The Mozilla Blog