Firefox 47.0 (64 bit)
Windows 10 Home (x64) Version 1511 (build 10586.420)
Both
Does not matter. Actually starting from the desktop shortcut is very slow (with no target web site).
No difference.
Actually on the same computer, same version of the browser works fine from another user login.
The problem only happens with one id, the administrator.
I have not done this.