Here is a list of useful Twitter Browser Tools

• iTweet – Browser tool for Twitter! Built-in auto-refresh, URL inline with tweets, notifications features, view user bio, search and hashtags, full follow, block, location, watch conversations with “in reply to” links.
• iTwitter – The iGoogle iTwitter Tab instantly creates a personal “Twitter Workbench” for maximizing your Twitter productivity directly within iGoogle.
• Matt – Multiple account twitter tweeting. Matt makes it easy to post to multiple Twitter accounts without having to log into each one every time.
• TwitBin – Send and receive messages to all your fellow twitterholics, right from your firefox browser. (This is COOL)
• TwitKit – TwitKit is a Twitter sidebar for Firefox.
• Twitter Search Bar – This script will add a search form and list of hot topics as a banner on Twitter.com.
• TwitterBar – TwitterBar is an extension for the Mozilla Firefox Web browser that allows you to post to Twitter from the Firefox address bar. Just type your tweet in the address bar and click the TwitterBar icon to send it to Twitter…
• TwitterKeys – Enhance your Twitter conversations with fun html characters using this super awesome tool!
• TwittyTunes – TwittyTunes is a FoxyTunes companion Firefox extension – it allows you to post your currently playing songs to Twitter with a click.
• Twummize – Twitter and Summize (Twitter search) in one window.