I did a search and didn't find this so here goes...
I wanted to force Messenger to use my default browser instead of IE when I clicked the check my inbox button.
I downloaded Messenger Plus 3 from
http://www.msgplus.net/ and installed it. Then I installed the Stuffplug NG plugin
http://www.stuffplug.com/ for Messenger Plus, and configured it to force messenger to use my default browser. Now MSN is using Firefox with no problems.
