IIS: Internet Information Services Default Username and Password

After re-installing Microsoft Visual Studio .NET on my new laptop, I decided to play around with IIS. I am very experienced with Apache but totally new to IIS. After installing IIS for development, I tried to go to http://localhost in Firefox and was prompted for a password. Obviosuly, since I didn't set the password in first place I had no idea what password/user it is talking about. A lit bit of Googling revealed that the default username is IUSER_ComputerName where ComputerName is the name of your computer. So in my case the username was IUSER_Alhumdulillah. Now I know the username but what about the password? So I opened up "Computer Management" screen by going to Start > Run and typing

compmgmt.msc \s

There I navigated to Internet Information Services folder, then right clicked on Default Web Site and selected "Properties". Once another window popped up, I clicked on Directory Security and then modified the passwords using the Edit function.

However my next attempt again failed to login using Firefox, even after a restart.

When I tried using IE, I got through.

References:
Default IIS username