Most people don’t realize it, but Firefox will do NTLM (Windows pass-through) authentication just like Internet Explorer. Some people solve the issue by going around Firefox and hosting IE right in Firefox. The other way to do it is to keep Firefox as the rendering engine and tell Firefox it’s OK to use Windows credentials to authenticate with a given site.

The problem is that managing the list of sites you allow Firefox to pass-through authenticate with is not straightforward and involves manually manipulating configuration settings.

This add-on makes it easier to manage this list, allowing you to stick with Firefox but still use Windows pass-through authentication.

Right now it simply adds an item to your Tools menu that gives you a first-class interface toward managing the list of sites. There are some other things I’m thinking about doing, but you can check all that out on the project site. If you want to try it out, you can get it on the Mozilla site.