Webmail Access Fails with SeaMonkey Browser

I usually use my SeaMonkey browser to access my Cox Webmail to mark the spam messages the Cox filter misses before I download new messages with SeaMonkey Mail.  SeaMonkey Mail still accesses the account normally; but starting today, after I enter my address and password on the Cox Webmail sign-in page I get a new pop-up saying "Authentication Required" and "https://myemail.cox.net is requesting your username and password. The site says: “OX WebDAV”.   Even if I re-enter the username and password, the same pop-up returns, blocking my webmail access.

Edge browser accesses the webmail page normally.

Can anyone suggest what may have changed to cause this issue and what might be done to correct it?