@daniel you can use it to submit data to a script just as you're submitting a form, automatically. This script sends his request as a Firefox user, so it can bypass a filtering by User-Agent.
But it becomes useless if the receiving script expects also a captcha or a CSRF value.
The usage is simple:
$random=rand(1, 100000);
$cookie=$random . ".txt";
$agent="Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)";
# where to submit data
$url = 'http://website.tld/data.php';
# the page from which is supposed to submit data
# this is fake information, just as User-Agent
$referer = 'http://website.tld/form.php';
# form input fields and values to submit
$vars = array(
'field_name_1' => 'value 1',
'field_name_2' => 'value 2'
);
echo post($url, $referer, $agent, $cookie, $vars);
bye.