After months of using Mozilla and getting hooked on 'tabbing' web pages (as explained in this hint), my biggest frustration was the apparent lack of a keyboard shortcut to switch between tabs.
After numerous web searches and browsing the Bugzilla bug database on mozilla.org, I'd just about given up hope of finding a shortcut. Then tonight, a friend casually mentioned that you can switch tabs using control page-up (previous tab) and control page-down (next tab).
Wonderful!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020322011041293