using javascript to determine ip works in chrome not firefox or ie

I am using javascript to determine the visitors ip address. For what ever reason, it works in Chrome and not in Firefox, IE, or other browsers.

Here is my code:

function getIPAddress() {
    var xmlHttp;

    if (window.XMLHttpRequest) {
        xmlHttp = new XMLHttpRequest();
    } else {
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    }

    xmlHttp.open("GET", "http://api.hostip.info/get_html.php", false);
    xmlHttp.send();

    var hostipInfo = xmlHttp.responseText.split("\n");

    for (var i = 0; i < hostipInfo.length - 1; i++) {
        var ipAddress = hostipInfo[i].split(":");
        if (ipAddress[0] == "IP") return ipAddress[1];
    }

    return "unknown";
}

At the company I'm working for, I am behind a proxy. Could this be a proxy issue, or is there something wrong with this code? Thanks.

Just deployed my code to our test environment, and in IE, I receive a pop up saying 'This page is accessing information that is not under its control. This poses a security risk. Do you want t开发者_StackOverflow社区o continue?' If I say, yes, it works. If I say, no, it doesn't.

If you're going to use AJAX (which is what this code is), I STRONGLY suggest you use a 3rd party wrapper like jQuery. That will increase cross-browser compatibility greatly and allows you to shrink your code down to something like this.

$.post('http://api.hostip.info/get_html.php', function(data){
    alert(data);
});

Additional Point

As Pointy mentioned, if your page is running on a different domain than hostip.info, you will need to setup a local PHP to fetch the data like this..

localGetData.php

die(file_get_contents('http://api.hostip.info/get_html.php'));

New Ajax

$.post('localGetData.php', function(data){
    alert(data);
});

for (var i = 0; i < hostipInfo.length - 1; i++) { will cause to return "unknow" if hostipInfo has only one element, change to for (var i = 0; i < hostipInfo.length; i++) {.

The reason this works in Chrome is because it supports CORS which allows you to make this request cross domain.

Since the site doesnt appear to support