event.php

<?php
header("Content-Type: text/event-stream\n\n");

echo 'data: ' . json_encode(
                  array(
                    0 => array(
                      'time' => time(),
                      'message' => 'Some kind of foo'
                    ),
                    1 => array(
                      'time' => time(),
                      'message' => 'Some kind of quux'
                    )
                  )
                ) . "\n";

?>

firefox-event-source.html

<script src="firefox-event-source.js"></script>
<script>
console.log(EventSource);


var eventSource = new EventSource('event.php');

console.group('eventSource')
  console.log(eventSource);
  console.log(eventSource.constructor);
console.groupEnd();

eventSource.addEventListener('open', function (event) {
  console.log('OPEN!');
}, false);

eventSource.addEventListener('message', function (event) {
  var message = JSON.parse(event.data);
    console.log(message);
}, false);


</script>

firefox-event-source.js

	;(function (w) {
		  if ( !w['EventSource'] ) {
		    // parseUri 1.2.2
		    // (c) Steven Levithan <stevenlevithan.com>
		    // MIT License

		    // including fixes by benjchristensen to make it fire a separate event for each message received rather than grouping them 
		    // all together (since JSON.parse was not working with the received messages in the original since multiple JSON messages 
		    // were all being combined into one event)

		    var parseUri = function(str) {
		      var o = {
		          key: ['source','protocol','authority','userInfo','user','password','host','port','relative','path','directory','file','query','anchor'],
		          q: {
		            name: 'queryKey',
		            parser: /(?:^|&)([^&=]*)=?([^&]*)/g
		          },
		          parser: {
		            strict: /^(?:([^:\/?#]+):)?(?:\/\/((?:(([^:@]*)(?::([^:@]*))?)?@)?([^:\/?#]*)(?::(\d*))?))?((((?:[^?#\/]*\/)*)([^?#]*))(?:\?([^#]*))?(?:#(.*))?)/
		          }
		        },
		        m = o.parser.strict.exec(str),
		        uri = {},
		        i = 14;
		      
		      while (i--) uri[o.key[i]] = m[i] || '';
		      
		      uri[o.q.name] = {};
		      uri[o.key[12]].replace(o.q.parser, function ($0, $1, $2) {
		        if ($1) uri[o.q.name][$1] = $2;
		      });
		      
		      return uri;
		    };
		        
		    
		    // EventSource implementation
		    function EventSource( resource ) {
		      
		      var that = (this === window) ? {} : this,
		          retry = 1000, offset = 0,
		          boundary = "\n", queue = [], origin = '',
		          lastEventId = null, xhr = null, source = null, matches = null, resourceLocation = null;
		      
		      that.toString = function () { return '[object EventSource]' };
		      
		      // EventSource listener
		      that.addEventListener = function (type, listener, useCapture) {
		        document.addEventListener(type, listener, useCapture);
		      };
		      // EventSource dispatcher
		      that.dispatchEvent = function (event) {
		        document.dispatchEvent(event);
		      };
		       
		      resourceLocation = parseUri(resource);
		      
		      // same origin policy
		      if ( resource.match(/http/) && resource.match(/http/).length ) {
		        if ( resourceLocation.host !== location.host ) {
		          throw DOMException;//"SECURITY_ERR: DOM Exception";
		        }
		      }
		      that.URL = resourceLocation.source;
		      
		      var openConnectionXHR = function() {
		          
		        xhr = new XMLHttpRequest();
		        xhr.open('GET', that.URL, true);

		        // FIRE OPEN EVENT
		        var openEvent = document.createEvent('UIEvents');
		            openEvent.initEvent('open', true, true);
		            openEvent.origin = document.domain;
		            openEvent.source = null;
		            that.dispatchEvent(openEvent);
		        
		        
		        if ( lastEventId ) {
		          xhr.setRequestHeader('Last-Event-ID', lastEventId);
		        }
		        xhr.onreadystatechange = function() {
		          switch (xhr.readyState) {
		            case 4: // disconnect case
		              pseudoDispatchEvent();
		              reOpenConnectionXHR();
		              break;
		            case 3: // new data
		              processMessageFromXHR();
		              break;
		          }
		        }
		                 
		        xhr.send(null);
		      }

		      var reOpenConnectionXHR = function() {
		        xhr = null;
		        offset = 0;
		        setTimeout(openConnectionXHR, 1000);
		      }
		  
		      var processMessageFromXHR = function() {
		        var stream = xhr.responseText.split(boundary);
		        // Abandon if empty
		        if ( stream.length < offset ) {
		          return;
		        }

		        for ( var i = 0; i < stream.length; i++ ) {
		          queue.push(stream[i]);
		        }
		        
		        pseudoDispatchEvent();
		      }
		  
		      var pseudoDispatchEvent = function() {
		        var name = 'message';
		        
		        queue.reverse();
		        
		        while (queue.length > 0) {
		        	var data = '';
			          line = queue.pop();
			          var dataIndex = line.indexOf(':'), field = null, value = '';
			            
			          if (dataIndex == -1) {
			            field = line;
			            value = '';
			          }
			          else if (dataIndex == 0) {
			            // Ignore Comment lines
			            continue;
			          }
			          else {
			            field = line.slice(0, dataIndex)
			            value = line.slice(dataIndex+1)
			          }
			          
			          if (field == 'event') {
			            name = value;
			          }
			            
			          if (field == 'id') {
			            lastEventId = value;
			          }
			          
			          if (field == 'retry') {
			            value = parseInt(value);
			            
			            if (!isNaN(value)) {
			              retry = value;
			            }
			          }
			          
			          if (field == 'data') {
			            if (data.length > 0) {
			              data += "\n";
			            }
			                
			            data += value;
			          }
			          
			        var fireEvent = document.createEvent('UIEvents');
			        // MessageEvent causes "setting a property that has only a getter" Errors
			      
			        
			        if ( data.length > 0 ) {
			          
			          fireEvent.initEvent(name, true, true);
			          fireEvent.lastEventId = lastEventId;
			          fireEvent.data = data.replace(/^(\s|\u00A0)+|(\s|\u00A0)+$/g, '');
			          fireEvent.origin = document.domain;
			          fireEvent.source = null;
			          that.dispatchEvent(fireEvent);
			        }
			        
		        }// end of while loop
		      }

		      // INIT EVENT SOURCE CONNECTION
		      openConnectionXHR();
		    };
		    window['EventSource'] = EventSource;
		  }
		})(window);