At a minimum, you're missing a dash between Firefox and >new. Let's assume that was introduced while typing into the perlmonk form. I don't have Firefox installed, so I can't help further.
in reply to RemoteObject.pm fails in open firefox8.0
$ffpath='C:\\Program Files\\Mozilla Firefox\\firefox.exe';
$mech = WWW::Mechanize::Firefox->new(
file for MozRepl::RemoteObject lists Firefox 7 Beta 5 as the most recent browser tested.
+ The module is now tested with
Firefox 7 Beta 5