use strict;
use warnings;
use POSIX;
use constant TIMEOUT => 20;

my $firefox;
unless ($firefox = fork) {
  die "Failed to fork: $!" unless (defined $firefox);
  exec '/woimmer/ich/bin/firefox', 'http://www.example.com/';
  die "Failed to spawn firefox: $!";
}
else {
  # remember time the browser was started
  my $start = time;
  my $remaining = TIMEOUT;

  # only loop while the browser is still running and the timeout is not over
  while (waitpid($firefox, WNOHANG) < 0 and $remaining > 0) {
    sleep $remaining;
    $remaining = $start + TIMEOUT - time;
  }

  # send the browser a TERM signal
  kill TERM => $firefox;
  # clean up the zombie process
  die "Problems cleaning up the browser process: $!" if (waitpid($firefox, 0) < 0);
}