It would not solve the authentication problem, but you can use command line ftp to download Firefox from a new installation, assuming it's available or can be

It would not solve the authentication problem, but you can use command line ftp to download Firefox from a new installation, assuming it's available or can be installed with Windows setup. Start command prompt. Enter ftp ftp.mozilla.org ftp ftp cd /pub/firefox/releases/latest/win32/en-US/ get "Firefox Setup 27.0.1.exe" There is a stub installer in the same directory, which will download the full package and install it, if you prefer.