CodeIgniter Issue with Uploadify

I spent whole day on finding solution but could not.I have simplified my code to find issue but could not found. The same code working in Chrome but not in FireFox.

ERROR (some time getting one error some time other)

IO error
HTTP error 303
Here is my code

Code:

$('#file_upload').uploadify({
        'swf'      : '<?php echo base_url();?>uploadifyit/uploadify.swf',
        'uploader' : '<?php echo site_url()?>/rentals/rental_imageUpload',
        'onError' : function(event, queueID, fileObj, errorObj) { alert(errorObj.type + ' ' + errorObj.info ); }
        // Your options here
    });

My Controller function is

Code:

public function rental_imageUpload(){
    echo 1;
}