Quick and dirty Appcelerator Alloy + FireFoxOS hack. This sample App works EXACTLY the same on iOS, Android and FirefoxOS.

index.js

function onsuccess(data){
	var jdata=JSON.parse(data);
	
	var data=[];
	jdata.forEach(function(item){
		var payload={
			tweet:item.text
		};
		
		var row=Alloy.createController('tweet.row',payload).getView();
		data.push(row)
	})
	$.tweets.setData(data);
}

var url='https://api.twitter.com/1/statuses/user_timeline.json?include_entities=true&include_rts=true&screen_name=appcelerator&count=20';

if (OS_MOBILEWEB){
	(function(url,callback){
		var xhr = new XMLHttpRequest({mozSystem: true});
		xhr.open("GET", url, true);
		xhr.onreadystatechange = function () {
			if (xhr.status === 200 && xhr.readyState === 4) {
		    	callback(xhr.response);
			}
		}
		
		xhr.onerror = function () {
			alert("Result from Cross-domain XHR: Cross-domain XHR failed");
		};
		xhr.send();		
	})(url,onsuccess)
}else{
	(function(url,callback){
		// do regular Titanium.Network.createHTTPClient
		var xhr = Ti.Network.createHTTPClient({
			 // function called when the response data is available
			 onload : function(e) {
			     callback(this.responseText);
			 },
		     // function called when an error occurs, including a timeout
		     onerror : function(e) {
		         alert('error');
		     },
		     timeout : 5000  // in milliseconds
		 });
		 // Prepare the connection.
		 xhr.open("GET", url);
		 // Send the request.
		 xhr.send();
	})(url,onsuccess)
}

$.index.open();

index.tss

".container": {
  backgroundColor:"white"
},
"Label": {
	width: Ti.UI.SIZE,
	height: Ti.UI.SIZE,
	color: "#000"
} 

index.xml

<Alloy>
  <Window class="container">
		<TableView id="tweets">
		</TableView>
	</Window>
</Alloy>

manifest.webapp

{
  "name": "FxOS01",
  "type" : "privileged",
  "description": "Ti HTTP Test",
  "launch_path": "/",
  "icons": {
    "128": "/appicon.png"
  },
  "developer": {
    "name": "Ricardo Alcocer",
    "url": "http://appcelerator.com"
  },
  "default_locale": "en",
  "launch_path" : "/index.html",
  "permissions": {
        "desktop-notification": {
            "description" : "To show notifications"
        },
        "systemXHR": {},
        "geolocation": {
            "description" : "Marking out user location"
        }
    }
}

tweet.row.js

var args=arguments[0] || {};

$.tweet.text=args.tweet;

tweet.row.tss

".container": {
  backgroundColor: "white"
},
"#tweetcontainer":{
	top: 5,
	bottom: 5,
	left: 5,
	right: 5,
	height:100,
	borderRadius:5,
	borderWidth: 1,
	borderColor: "#cacaca"
},
"#tweet":{
	height: Ti.UI.SIZE,
	width: Ti.UI.FILL
}

tweet.row.xml

<Alloy>
  <TableViewRow id="tweetrow" height="Ti.UI.SIZE">
		<View id="tweetcontainer">
			<Label id="tweet"/>
		</View>
	</TableViewRow>
</Alloy>

The important stuff: You need to include in your manifest.webapp two entries:

"type" : "privileged"

"type" : "privileged"

(look above)

Once you've done that, make sure that you instantiate your XMLHTTPConnection with an extra parameter:

var xhr = new XMLHttpRequest({mozSystem: true});

That takes care of allowing you to make HTTP request outside of the sandbox. Other than that, it's just Titanium and Alloy.

Fun times!!!

This is how it looks:

And Running on iOS

Get the Firefox OS Simulator at https://hacks.mozilla.org/2013/05/firefox-os-simulator-3-0-released/