Mac: Tabbing through all form fields
By default, the Mac OS X behavior for tabbing through form fields is different than that of Windows and Linux. Instead of tabbing through all fields in a form, the default Mac behavior is to skip only between lists, text fields and text areas. Buttons and checkboxes are skipped. However, this behavior is configurable.
To configure OS X to tab through all fields, go to System Settings and navigate to Keyboard and Mouse. From there, click on the Keyboard Shortcuts at the top.
At the bottom of the Keyboard Shortcuts screen is a pair of radio buttons under the heading Full Keyboard Access. The second option, All Constrols, changes the tabbing behavior to include all form elements.