Error in uploading csv file in mozilla

[eluser]rampelli[/eluser]
while uploading a csv file using CI 1.7.1 it is working good in

internet explorer and google chrome but i am getting error in Mozilla 3.5.3 browser

The filetype you are attempting to upload is not allowed.

can any one help me .. to get out of this problem

below is my code

Code:

$config['upload_path'] = './uploadpath/csv/';
        $config['allowed_types'] = 'csv';
        $config['max_size']    = '5000';
        $this->CI->load->library('upload', $config);
    $this->CI->upload->do_upload('file')