Power Twitter adds features to the Twitter Web interface including:

-search and recent searches
-search scoped to a specific user
-status history peeking on mouseover
-Facebook status updates
-inline YouTube, Flickr, TwitPic, Google Maps, song.ly, and more
-url expansion
-url translation to page titles
-open web update (news feed) mapping
-custom settings
-@mentions
-photo uploading
-link shrinking
-#hashtags
Works with:

  • Firefox: 1.5 ? 3.0.*

https://addons.mozilla.org/en-US/firefox/addon/9591