[gentoo-user] Firefox-57.0.4 won't accept TLS certificate exception

[Mick]

I just noticed I am not able to override FF's protestations about the domain 
name of the loaded TLS certificate not matching the visited domain.  When I 
click on Advance/"Confirm Security Exception" to permanently store this 
exception nothing happens.  All I can do thereafter is cancel this pop up 
window.  Of course the page will not load.

How can I overcome this intransigence by the browser, who thinks it knows 
better what I wish to do?
-- 
Regards,
Mick