I downloaded Fire and it's working just fine for me. All I did is uncompress the files in the archive (gunzip -xvzf filename) from the terminal command line, and it extracted to a folder which I copied to the applications location. I then double clicked on Fire and it started right up.
I downloaded and Installed Fire with gnutar -zxf and it crashed the first time, and I couldn't get it to work after that.
So I went to my preferences folder /users//library/preferences and threw away the Fire preference (I believe it was called fire.plist not sure though) and Started fire again, reset my prefs and it's been working fine ever since.
I had some problems with fire, but its mainly because StuffIt expander sucks. You have to decompress the file either from the command line or using a different expansion app like OpenUp (look for it at Stepwise.com). Although to decompress OpenUp you have to use the command line anyways, so... there are instructions for using the command line at the fire homepage.
Go to http://www.epicware.com/fire.html. There is a link to download a zip compressed .pkg file decompress w/ stuffit or the decompression utility of your choice and run the .pkg file. It will open the installer.app.
This version works fine for me with aim and yahoo. .