ESSENTIAL Webmasters Tools we can't live without
Spoon Browser Sandbox
Your site/design simply has to work in all the browsers, but since you can only install one version of most browsers at a time (notably, Explorer), how can you test for all possible browsers AND versions? Simple ... head over to Spoon, you can run ANY browser in a virtualized "sandbox". No installation required. No fee for use. This
is the holy grail, folks.
Spoon.net/Browsers/
Website Testing
Success in web design and user experience depends on you getting it right and keeping it right. How are you currently doing QA? Fix. Reload. Look Around. Repeat. Automate the 'Look Around' process with Selenium. We setup every web page with a test using Selenium IDE so that as we make changes we can simply re-run the tests and make sure that everything still works the same. It's the only way to be sure.
Selenium
Code Validation and Testing
The Essential Plugins for Firefox
For starters, if you're developing websites, you need to be using Firefox. Aside from being the best "pure" and compliant browser available, the extensive number of plugins for web developers will make your web development life MUCH easier.
