Power twitter is a Firefox add-on that enhances twitter with a search box on twitter timeline and with other nifty features. If you use twitter a lot install this add-on to get most out of twitter.
After installing the addon, it adds a twitter search box to the page, you can directly search with this box and the results are displayed on the same page. When you visit other twitter user pages it allows you to search only that user tweets which is really helpful. Other important features of this extension is it adds the page title of the link you are about to follow, so you will know where you are going.
It also displays Flickr pics, YouTube videos, twitpic pics inline, you don’t have to click to see that pic your friend has sent you. When you hover your mouse on friends avatars it shows their recent activity.
Download the extension from here.