jquery.getActiveMQ.js

(function($,window){
  
  window.getActiveMQ = function()
	{
		$('<div id="getActiveMQ-watcher"></div>')
			.appendTo('body')
			.hide();
	
		var computed = window.getComputedStyle,
			watcher = document.getElementById('getActiveMQ-watcher');
			if ( 'currentStyle' in watcher )
			{
				window.getActiveMQ = function()
				{
					return watcher.currentStyle['fontFamily'].replace(/['"]/g,'');
				};
			}
			else if ( computed )
			{
				window.getActiveMQ = function()
				{
					return computed( watcher, null ).getPropertyValue( 'font-family' ).replace(/['"]/g,'');
				};
			}
			else
			{
				window.getActiveMQ = function()
				{
					return 'unknown';
				};
			}
			return window.getActiveMQ();
	};

}(jQuery, window))

sample-getActiveMQ-setup.css

#getActiveMQ-watcher {
  font-family: "break-0";
}
@media only screen and (min-width: 20em) {
  #getActiveMQ-watcher {
    font-family: "break-1";
  }
}
@media only screen and (min-width: 30em) {
  #getActiveMQ-watcher {
    font-family: "break-2";
  }
}
@media only screen and (min-width: 48em) {
  #getActiveMQ-watcher {
    font-family: "break-3";
  }
}
/* etc. */