Perl Mechanize-optimizaztion: make a script running faster with less overhead

[Perlbeginner1]

dear monks - this is the thread for the: Perl Mechanize-optimizaztion: make a script running faster with less overhead

Problem: I have a list of 2500 websites and need to grab a thumbnail screenshot of them. How do I do that? I could try to parse the sites either with Perl.- Mechanize would be a good thing. Note: i only need the results as a thumbnails that are a maximum 240 pixels in the long dimension.

Prerequisites: https://addons.mozilla.org/en-US/firefox/addon/mozrepl/
the module WWW::Mechanize::Firefox;
the module imager http://search.cpan.org/~tonyc/Imager-0.87/Imager.pm

First Approach: Here is a first Perl solution:

  use WWW::Mechanize::Firefox;
  my $mech = WWW::Mechanize::Firefox->new();
  $mech->get('http://google.com');

  my $png = $mech->content_as_png();

Outline: This returns the given tab or the current page rendered as PNG image. All parameters are optional. $tab defaults to the current tab. If the coordinates are given, that rectangle will be cut out. The coordinates should be a hash with the four usual entries, left,top,width,height.This is specific to WWW::Mechanize::Firefox.
As i understand from the perldoc that option with the coordinates, it is not the resize of the whole page it's just a rectangle cut out of it.... well the WWW::Mechanize::Firefox takes care for how to save screenshots. Well i forgot to mention that i only need to have the images as small thumbnails - so we do not have to have a very very large files...i only need to grab a thumbnail screenshot of them. I have done a lookup on cpan for some module that scales down the $png and i found out Imager
The module does not concern itself with resizing images. Here we have the various image modules on CPAN, like Imager. http://search.cpan.org/~tonyc/Imager-0.87/Imager.pm
Imager - Perl extension for Generating 24 bit Images: Imager is a module for creating and altering images. It can read and write various image formats, draw primitive shapes like lines,and polygons, blend multiple images together in various ways, scale,crop, render text and more. I installed the module - but i did not have extended my basic-approach

What i have tried allready; here it is:

#!/usr/bin/perl

use strict;
use warnings;
use WWW::Mechanize::Firefox;

my $mech = new WWW::Mechanize::Firefox();

open(INPUT, "<urls.txt") or die $!;

while (<INPUT>) {
        chomp;
        print "$_\n";
        $mech->get($_);
        my $png = $mech->content_as_png();
        my $name = "$_";
        $name =~s/^www\.//;
        $name .= ".png";
        open(OUTPUT, ">$name");
        print OUTPUT $png;
        sleep (5);
}

Well this does not care about the size:
See the output commandline:

linux-vi17:/home/martin/perl # perl mecha_test_1.pl
   www.google.com
    www.cnn.com
    www.msnbc.com
command timed-out at /usr/lib/perl5/site_perl/5.12.3/MozRepl/Client.pm
+ line 186
linux-vi17:/home/martin/perl #

This is my source ... see the

urls.txt 
www.google.com
www.cnn.com
www.msnbc.com
news.bbc.co.uk
www.bing.com
www.yahoo.com

Question: how to extend the solution either to make sure that it does not stop in a time out. and - it does only store little thumbnails

Note:again: i only need the results as a thumbnails that are a maximum 240 pixels in the long dimension.
As a prerequisites, i allready have installed the module imager http://search.cpan.org/~tonyc/Imager-0.87/Imager.pm
love to hear from you!