Sure.

my $i = 0;
for my $url (@urls) {
    my $outfile = sprintf "screenshot-%02d.png", ++$i;
    system 'firefox', $url;
    system "xwd | xwdtopnm | pnmtopng > $outfile";
}
[download]

After the page is fully loaded, click the firefox window. Adding e.g. gimp to that loop to convert the PNG file to JPEG is left as an exercise to the reader ;-)