Running Acer laptop Win7 Home edition, Avira Antivirus, Windows Firewall. Downloaded Firefox installer stub from Mozilla. On running it, it says 'extracting' then shows a message saying "Some facilities may not work installing with current user" and shows two options: Run with current user and Administrator (password to be filled only for Administrator). Click on current user and the program disappears - nothing happens. There is only 1 user profile on this system - current user, called 'a' with administrator rights and no password. Clicking on Administrator insists on password, will not accept blank password field and disappears. I created an Administrator ID with password and logged in but the same two options again pop up - and the same disappearance of the program once either is chosen. Tried with Avira and Firewall disabled. Makes no difference. Was running Firefox earlier version with current user profile and no problems. When program upgraded itself, this problem has started so that I have to use IE or Chrome. I'm typing this from my desktop system where Firefox is running fine.