...
$mw->minsize(700,400);
...
my $c1 = $scrolledMListbox->columnInsert('end',  -text => 'Path');
$c1->configure(-width => 25);
my $c2 = $scrolledMListbox->columnInsert('end', -text => 'Modified');
$c2->configure(-width => 25);

my $c3 = $scrolledMListbox->columnInsert('end',  -text => 'Dir');
$c3->configure(-width => 25);
my $c4 = $scrolledMListbox->columnInsert('end',  -text => 'File');
$c4->configure(-width => 25);