Zend certified PHP/Magento developer

how can I make mozilla FF start downloading whatever media are on the page

Suppose I have a web page which contains a button which when pressed, my Fire Fox starts replaying
some mp4 file. What can I do about the configuration of my Mozilla browser so that instead of replaying the audio file it starts downloading it ?
Shall I use some specific Add-on or rather touch something in the about:preferences
page ?