I'm pretty tired (Friday and all) so I may not be wrapping my head around this properly, but won't grep /\Q$_/, @wf just be matching the elements of @wf against themselves, and not @f like you probably intended?

for my $ff (@f) {
    if (! grep {$ff=~/\Q$_/} @wf){
        print "$ff\n";
    }
}
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