You can host any standard ActiveX control in a new tab in the Resource Manager. The trick for you would be to find a control that is a web browser that is not IE if you need to use something else.
Here's a JScript sample that creates a new tab with IE in it for reference:
//XMetaL Script Language JScript:
try {
ResourceManager.AddTab("My Browser","Shell.Explorer");
}
catch(e){
//Silent fail (tab already exists).
}
var browser = ResourceManager.ControlInTab("My Browser")
if (browser) {
var url = "http://forums.xmetal.com";
browser.Navigate(url);
}