I always tell students to use the Web Developer Toolbar developed by Chris Pederick. It’s free, it works in Firefox, Opera, or Chrome and it’s very helpful.
This short video explains a bit about it. Although it’s talking about Joomla specifically and is an ad for Lynda.com, it’s still a good video. You hear Jen Kramer doing the description. It’s almost the same speech that I give students when I introduce them to this tool, so I thought it was worth sharing with you.