Today, the new versions of both FireFox and Thunderbird were released.
FireFox 0.8 (Previously known as FireBird) has recieved some major updates, it now has an installer included with it, the download manager has been redisigned and many more usefull things, check this for all details.
Also ThunderBird 0.5 was released today, containing some major updates like support for multiple identities per e-mail account, improved spell checking, and many more! You can check out what's new here.