"i tried very hard on google to find the solution for the installation"

The first place I'd check would be the module documentation. Read and understand WWW::Mechanize::Firefox::Installation, WWW::Mechanize::Firefox::Troubleshooting and WWW::Mechanize::Firefox::FAQ. PPM::Repositories has a list of all known repos. Consider installing via cpan (after you've read the module documentation):

c:\>cpan WWW::Mechanize::Firefox
[download]