I’ve been a Mac user for just about a year now (couldn’t ever go back), but I’ve noticed an annoying little “feature” within Firefox that I was never able to resolve until recently. While tabbing through form fields, drop-downs are skipped and require switching to the mouse to set a value.
Turns out the issue is pretty simple to resolve. Go to System Preferences, then select Keyboard. On the bottom of the window there is a section titled ‘Full Keyboard Access’ (as pictured below).

Simply change the option to ‘All controls’ instead of the default. This will allow you to tab between all elements on the page. In addition to drop-downs, you will now be able to focus on links as well.
Tip: The keyboard shortcut Control +F7 will toggle this setting if you prefer to enable/disable it quickly.
A big nod goes to howtogeek.com for this fix.
