A user reported that the page that comes up when visiting an untrusted
https site does not show the expected instructions about using 'M-x
ssl-add-exception'. It is a different page entirely, and although it has
a button to add an exception, the button does not work.
Currently, conkeror adds that message about 'M-x ssl-add-exception' via
entities in locale/en-US/netErrorApp.dtd. What we could do instead is
override the whole page with our own. It would provide better
instructions than even the normal one.