Most people don't realize it, but Firefox will do NTLM (Windows pass-through) and SPNEGO (Kerberos, etc.) 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 integrated/pass-through authentication.
The extension uses the Firefox Add-On SDK for build/execution. You can get the SDK from the Mozilla site.
To start the SDK, run C:\firefox-addon-sdk\bin\activate - this sets up the environment. You then have some commands available:
cfx run - Launches Firefox with the extension loaded in a test profile.
cfx xpi - Packages the add-on into an XPI file for publication.
There are some convenience batch files (start-addin.bat and build-addin.bat) that do the SDK start/run all in one click.