Add the following line to /etc/apt/sources.list

deb http://dl.ubnt.com/mfi/distros/deb/debian debian ubiquiti

Add GPG keys

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv C0A52C50

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10

Update the system

sudo apt-get update

Install the mFi software

sudo apt-get install mfi

Once it is finished installing you should be able to browse to https://yourserverip:6443 to access the mFi web page.