- [Firebug] (http://getfirebug.com/) - set of development tools which makes developer’s life easier
- [Measurelt] (https://addons.mozilla.org/en-us/firefox/addon/measureit/) - draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels
- [HttpRequester] (https://addons.mozilla.org/en-us/firefox/addon/httprequester/) - a tool for easily making HTTP requests (GET/PUT/POST/DELETE), viewing the responses, and keeping a history of transactions
- [Stylish] (https://addons.mozilla.org/en-US/firefox/addon/stylish/) - A tool to add custom styles for web pages. I personally use it to color the background of open tabs so I can distinguish which of the tab is development/test/accepptance/production version.
- [Ripple emulator] (https://chrome.google.com/webstore/detail/ripple-emulator-beta/geelfhphabnejjhdalkjhgipohgpdnoc) - multi-platform mobile environment emulator that is custom-tailored to mobile HTML5 application development and testing