MD5 is way outdated. You should use Digest::MD5 instead. This makes it

use Digest::MD5 qw(md5_hex);

...

my $fileMd5 = md5_hex($text) . $ext;
[download]

As a minor nit, I advise to use the three-argument form of open whenever possible (ie when you're not working with pipes; that is planned for a later version of Perl5 too though) for a variety of reasons. No, they don't really apply here, but it's good habit.

open(my $fh, ">", $fileMd5) or warn("Could not create ($fileMd5)\n"), 
+next;
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And finally, for the Unixers out there using Mozilla, it can be adapted using the following code:

if(system(mozilla => -remote => 'ping()')) {
    warn "mozilla not found!";
    my $pid = fork;
    die "Couldn't fork: $!" if not defined $pid;
    exec { 'mozilla' } 'mozilla' if $pid == 0;
}

# and changing the command like so:
# (obviously, use "new-window" if you prefer that)

my $commandShow = q{mozilla -remote "openurl(%s, new-tab)"};
[download]

For the Windows Mozillaites, that will be something like this (but don't quote me on it, since I have neither used Win32::Process nor any desire to expand my experience with that OS):

Win32::Process::Create(
    my $process,
     "mozilla.exe", # maybe needs absolute path, dunno
    "",
    0,
    NORMAL_PRIORITY_CLASS,
    "."
) || die ErrorReport() if system(mozilla => -remote => 'ping()');
[download]

I also attached a patch for your downloadable script to make these changes (posted in a separate node to avoid confusion with the code blocks in this one).

Makeshifts last the longest.