Fire has recently announced an update to the latest Yahoo protocol. However, it is not likely to support MSN anytime soon. Microsoft, citing "security issues", has repeatedly forced me to update Messenger like four times this year on my Windows box, each version bringing everything but actual security improvements. Anti-firewall file transfers,banner ads, frilly (and space-wasting) dialog boxes, buddy photos, video and voice chat - they're all there, utterly useless features for corporate environments, where you only end up using IM for setting up lunch, swapping URLs and pieces of code.
(The notion that people spend half their work hours chatting with their significant others or squirrelling out corporate secrets one joke at a time is one of the most credible ruses ever crafted by the security solution spin doctors. IM is actually one of the most useful troubleshooting tools any IT department has - just try to read a complex URL or error message to somebody over the phone, and you'll know what I mean.)
Now Microsoft plans to shut third parties out of their IM network, re-enacting the AOL/MSN wars of couple of years back - only this time, they're the big fish. Oh, and their Mac OS X client is crap, too.
Fire is neat, simple, extremely consistent with the Mac OS X interface and a pleasure to use. Yahoo and MSN (the only IM services I use) look like overdesigned pieces of bloatware next to it. I don't want to have voice, video, colored text or even a gazillion new Britney Spears smileys - I just want IM to do what it's supposed to to: let me send snippets of text to people.
And the server side looks no better. Corporate IM is dead in the water (ever read a Microsoft success story about Exchange IM deployment? Me neither.), IRC is crap (but is starting to look pretty good compared to the mess we'll be in a month from now), and "mini-mail" (the habit of sending one-line mail messages around) is a hideous (and laggy) kludge.