turn on tab in page navigation on a Macintosh (affects FireFox and Safari, chrome ignores the system preference)
Go to the the Apple Menu (top left)
Go to System Preferences
Click on "Keyboard" Preferences
Click the Shortcuts Tab
At the bottom of the page, change "Full Keyboard Access..." to "All Controls"
Now you can use the tab key to navigate through page elements in both Safari and Firefox on Macintosh.