http://msnmsgr.mozdev.org/This is an extension that my mate, Benoit, has made. He will be planning to make it compatible with the Firefox browser.
If you're currently using Mozilla v1.4 and up, or Seamonkey v1.x, feel free to give it a try and let him know what you think of it. Any helpful feedback will be appreciated by Benoit.
As for me, I think it's a good idea. It will save me the hassle of having to load up MSN when I can easily do so on some browser.