Posted by Andrew.
Developed by Firebug Team.
Developed by Google.
Speed Tracer is a tool to help you identify and fix performance problems in your web applications. It visualizes metrics that are taken from low level instrumentation points inside of the browser and analyzes them as your application runs. Speed Tracer is available as a Chrome extension and works on all platforms where extensions are currently supported (Windows and Linux).
Developed by ChromeFans.
PageRank Status is a Chrome SEO extension for webmaster. With this extension, you can view the Google PageRank and Alexa Rank of the current web page, quick access to Whois, Alexa, backlinks and indexed pages in a popup window.
Developed by Ben Beckford.
Resolution Test changes the size of the browser window for developers to preview their websites in different screen resolutions. It includes a list of commonly used resolutions as well as a custom option for you to input your own.
Developed by David Boissonnault.
W3C (x)HTML Validator displays one of 3 icons (valid, invalid, processing) in navigation bar related to validity of (x)HTML document currently shown.
Developed by Carter Cole.
SEO Site Tools pulls PageRank, domain links and rank metrics, aggrigates social media reactions from Twitter, Facebook, Digg and SEO releated tags.
Developed by SEOHeap.com.
Domain Availability Checker checks the availability of a domain name. What's the point of going to another page when you can check it from your toolbar.
If you know more useful extensions for webmaster, please leave your comments! :)