Firefox is your friend

Firefox is a testers friend it really is. The extensions available are excellent and save a massive amount of time. Get Firefox from the right nav over there >>

Then add a few extensions to it >Tools>Add ons

These are must haves

Try the developer add on, its excellent, and lets you query all aspects of the page your testing. Also has a very handy overlay ruler tool for measuring page items.

Try the TAW add on, it's an accessibility extension that allows you to verify, with just a click, the accessibility of the Web sites that you are visiting, by means of the TAW3 online service (www.tawdis.net) and making use of the W3C Web Content Accessibility Guidelines (WCAG 1.0).

Try the HTML validator - never let a dodgy coded page out of your sight again.