Power Twitter is an add-on for Firefox that takes regular Twitter and gives it mag wheels, a spoiler and a brand new engine. 

After installing Power Twitter and restarting your browser, your Twitter page will have these new features:

1) inline embedded media from Flickr, YouTube, TwitPic and others
2) expanded URLs so you can see where links might take you
3) twitter search and search results right on the page
4) peek – an avatar mouseover that lets you see recent tweets from that person
5) status updates that are happening with your friends on Facebook
6) when possible additional web updates (Flickr, blogs, etc.) for certain users

Power Twitter is yet another great free contribution to the Twitter community from very talented developers.

Find out more about it at http://83degrees.com/post/Adding_Features_with_Power_Twitter