Unfortunately Firefox didn't create a mac friendly version of their latest model so going to mozilla.com won't do anything for you. Best bet would be to try something like filefront. I think I can post the link here as it doesn't cost to use but I'm sorry in advance if I can't.

Here's the link
http://files.filefront.com/Firefox+1...einfo.html/1/1

If the mods find that offensive just google 'filefront firefox mac'

The reason mozilla won't give you it is because it is an older version than the latest firefox for windows software. So there may be a few security issues with it, but it should at least allow you to use chat. Quite frankly, I feel that an out of date firefox is better than safari any day of the week.

Hope I helped!
Knighty-Knight