User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36

Steps to reproduce:

Change the server name (host) for an existing account. Prefs will have "hostname" as the old server address, and "realhostname" as the new address.

Connect to the server and see the "add security exception" dialogue.

Actual results:

The dialogue shows the value from "hostname" instead of "realhostname" in the location field. Clicking to confirm the security exception adds this incorrect value into cert_override.txt.

Thunderbird will not recognise that an exception exists and will continue to display the "add security exception" dialogue, never allowing a connection.

Expected results:

I think that realhostname should be used for certificate exceptions.

https://searchfox.org/comm-central/rev/a18b84093ce824cd90f76054da6885378bc390c8/mail/base/content/mailWindowOverlay.js#2943 ->
https://searchfox.org/comm-central/rev/a18b84093ce824cd90f76054da6885378bc390c8/mailnews/base/src/nsMsgMailNewsUrl.cpp#589

I suppose nsMsgMailNewsUrl.cpp would have to have it's own implementation that would use realhostname.