How Do I Ensure No Other Browser Windows Open

Place the following function into User.js of your test:

function KillBrowser()
{
    if (g_browserLibrary == "Chrome HTML")
    {
        Global.DoKillByName('chrome.exe');
        Global.DoKillByName('RapiseChromeProxy.exe');
    }
    else if (g_browserLibrary == "Firefox HTML")
    {
        Global.DoKillByName('firefox.exe');
        Global.DoKillByName('RapiseChromeProxy.exe');
    }
    else if (g_browserLibrary == "Internet Explorer HTML")
    {
        Global.DoKillByName('iexplore.exe');
    }
}

Then just call the KillBrowser function from  TestInit block of your test.