Can the Firefox password manager store and manage passwords for multiple sub-domains or different URLs in the same domain?

The Firefox password manager will happily store more than set of login details per domain (and realm), as long as you have different user names for each login.

I have a main Google account and two accounts on Google Apps systems, so three accounts on the www.google.com domain.

For mail.google.com/a/company1.com the login name is my first name, for mail.google.com/a/company2.com the login name is a nickname, and for the main www.google.com my login is my full email address.

All I do is either start typing the login name, and then select the correct one for the service from the list of three that Firefox has remembered, Firefox then happily fills in the password field for me. Have also used on some other websites that I have multiple accounts on.

Subdomains yes, urls on same domain, no, as far as I know.