Software Testing Tools Question:

The favorite extension of programmers everywhere, Firebug is one of the best applications around for debugging issues with front-end code and CSS. If there’s any image or style that’s out of line, checking it out with Firebug is the best response. It’s even possible to change styles within the extension to see how a website will actually appear in the browser.

Firebug integrates with Firefox to put a wealth of web development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

http://getfirebug.com/