Comment 3 for bug 595551

This isn't a password manager problem. Password manager only saves tha password
for the next time you need to login, so the next time mozilla is started
During one session, necko stores the credentials and reuses them the next time
the url is accessed.
Before, necko got the full credentials from calendar, and used them. Now it asks
password manager (or the user) the first time, and then caches them.

You could try to use https://username:password@domain/ as url. It is unsafe,
because the password is stored in plain text, but it has always been that way.