Vladimir Kornea:
Try use html_entity_decode()

$str = 'first=value&arr[]=foo+bar&arr[]=baz';
parse_str(html_entity_decode($str), $output);
print_r($output);

Array
(
    [first] => value
    [arr] => Array
        (
            [0] => foo bar
            [1] => baz
        )

)