I Like Shortcuts
I've been a fan/user of the Web Developer Toolbar extension for Firefox for quite a while, but I just happened across a really handy keyboard shortcut for it. Pressing Ctrl+Shift+C will open a new tab and show all of the CSS styles used for whatever page you're viewing. Not earth shattering or anything, but incredibly handy - much faster than viewing the source of a page, locating the style sheet URLs and opening those by hand. Just another reason Firefox rocks.