On
Use this code on the page load event of MS CRM  2011/2013

function ReadOnly ()
{
    var controls = Xrm.Page.ui.controls.get();
    for (var i in controls)
    {

        var control = controls[i];
        if (!control.getDisabled())
        {
            control.setDisabled(true);
        }
    }
}

SOURCE : mscrm.com