FireFox 52: "Your connection is not secure" - How to manage an exception ?

Hello all,

Today I tried to visit a website and got an SSL "Your connection is not
secure" page instead. After clicking the "Advanced" button I got the
information that the certificate was expired ("advanced" ? My foot).

Two things:

1) All I got was an "add exception..." button, when I would have liked a
"for this session only..." one. Is there any way to enable this ?

2) I /could/ add an exception, but there is no info there to where to manage
(read: remove) the exception afterwards (so I get the same warning the next
time I'm visiting that webpage), which makes me hesitant.

Where do I manage those /exceptions/ ? There is not mentioning of them
under tools - options -advanced - certificates.

Regards,
Rudy Wieser