Psi is a free, open source instant messaging application designed for the Jabber IM network (including Google Talk) compatible with Windows, Linux and Mac OS X.
If you're tired with the Jabber functionality of Empathy or Pidgin, both lacking lots of important features for this protocol, you should give Psi a try.
If you spend most of your computing life in Firefox, it makes sense to consolidate other online activities in your browser. There are extensions that can help you to do just that: you can manage your bookmarks with the del.icio.us extension, chat on IRC channels using Chatzilla, and read RSS feeds in Sage. Jabber instant messaging users have their own extension: the SamePlace, a nifty IM client that, besides the basic Jabber functionality, offers a few unique and useful features.