I use Mozilla Browser almost exclusively and there should be no issue. If there are login difficulties with vb3 it will be one of these things.
1. Browser is not setup to handle cookies
2. User has not installed the product with the correct vblicense number so login can not authenticate
3. Cookie settings do not match vb
so when you log in you will not be logged into both products since cookie are not aligned.
Is there a url and test login available so I can saw which issue this is?