Yesterday Bing announced the partnership between Mozilla Foundation and Microsoft to release a customized version of Firefox. The new custom version of Firefox comes with Bing as the default search engine and many other things.
Firefox with Bing offers the latest version of Firefox with Bing set as your home page and the default setting in the search box and AwesomeBar (where you can also type in queries as well as Web addresses). If you already have the latest version of Firefox, then you just need to download the Bing Search for Firefox Add-on to set the same preferences.
You can download Firefox with Bing at Firefoxwithbing.com