In version 3.1.1 we added a new option called “Fixed Footer”. This setting will not “fix” your footer per-se but will add a min-height to your #main container to keep your footer always at the bottom of the page. This isn’t something we really thought was necessary, but a lot of customers requested it so we added it requires very little overhead anyway ;)
This is located at Appearance > Customize > Footer.
Below is an example result with the setting enabled so you can see what it does.