Five useful Firefox plugins for web developers
ColorZilla allows you to select any part of a webpage and receive both RGB and Hexidecimal colour codes. If you have ever used the color dropper tool in photoshop it works the same as that.
The Total Validator plugin allows you perform multiple validations as well as take screenshots of your pages with ease. It even includes validation for HTML5.
Page Speed allows you to track how well your pages are optimized. It will give you a score out of 100 and list possible improvements to decrease the loading time.
Browser Window Resizer
Browser Window Resizer allows you to resize your browser window to a variety of sizes. This is ideal for viewing your website in different resolutions. The supported sizes are 640×480, 800×600, 1024×768, 1280×1024, 1600×1200.