How to Enable Accessibility on Mac OS X 10.10 Yosemite
Open System Preferences > Security & Privacy
If you don't see the app you're trying to authorize,
you can add them by using the [+] button or simply
drag and drop the app from Finder to add it.
How to Enable Accessibility on Mac OS X 10.9 Mavericks
Open System Preferences > Security & Privacy
If you don't see the app you're trying to authorize,
simply drag and drop the app from Finder to add it.
How to Enable Accessibility on Mac OS X 10.8 Mountain Lion
Open System Preferences > Accessibility
Check the box next to "Enable access for assistive devices"