in Portal 2.7.2 issue JBPORTAL-2320 was fixed - now the login-window in IE and FF is the same.
But with 2.7.2 there is a new issue: The login-window-elements have fixed widths, which in some language-packs doesn't work out.
The german word "benutzername" for username is too long to fit in one row with the input-element, so it's placed a row above.
Dunno, how these issues are handled in the rest of the user-interface-elements, so I can just indicate, that the current solution is still not perfect.
Thanks LeoLo, I reopened the issue to fix this. Now I remember why I didn't put a fixed width on the first iteration ;)