- Wheel Button: Command + Click
- Left Side Button: Control-page up
- Right Side Button: Control-page down
Other alternatives could include setting one of the side buttons to close a tab (command-w). I don't know if Mozilla offers a command to cycle windows (although it is built into OS X under Full Keyboard Access in system prefs -- it just isn't activated yet). Of course, if I could figure out a way to get Mozilla to always open new tabs instead of windows (for example from SlashDock) then I wouldn't have to cycle windows anymore...
If anyone else has figured out a good way to program the mouse for Mozilla or other Apps, let me know.

