The most frustrating aspect of using my Mac was having to click a button instead of tabbing over to it. At last, I finally found a solution!

Go to System Preferences > Keyboard & Mouse > Keyboard Shortcuts. In the bottom right corner, there's a radio button saying "All controls": select it.

Select 'All Controls' radio box

And that's it! You can now tab your way to buttons and drop down lists!

Let me end this by saying that having tab cover text boxes only is possibly the single stupidest option to be turned on by default.