This kind of information is always infuriating for me. TweetDeck has been bought by twitter and now in their FAQ about the redesign, we can read.
On the web
You can sign up and log into TweetDeck at http://web.tweetdeck.com. The initial version is built for Webkit browsers, so Safari and Chrome are supported. Support for Firefox and IE will be added soon!
Design for the Web not for a brand. The open Web for everyone will be a lot better.