The following code crashes my mIRC 6.16 and errors on mIRC 6.17
//comopen html htmlfile | !.echo -q $com(html,URL,4,bstr,www.mirc.com)
Making the bstr by reference does not make a difference.
Documentation about the url method: here
EDIT: first time I use mIRC in a few months and already forget there is a newer version. Though it doesn't crash anymore, it does spit out an error I've never encountered before.