Thanks. By reworking one of the examples I was able to put together a code which opens the Firefox browser, loads the CPAN search page, fills in the query field with 'WWW::Mechanize' and then submits the form:
#!/usr/bin/perl
use strict;
use warnings;
# the module we're looking for
my $module_name = 'WWW::Mechanize';
# create a new browser
use WWW::Mechanize::Firefox;
my $browser = WWW::Mechanize::Firefox->new(
launch => 'C:/Program Files/Mozilla Firefox/firefox.exe',tab=>'cur
+rent'
);
# tell it to get the main page
$browser->get("http://search.cpan.org/");
# submit the query form
$browser->submit_form(with_fields=>{query=>$module_name});
|