Firefox issue submitting twice

[budd]

ok so i found a way to encrypt part of a url to stop people editing it

 

/**
* Encrypt/decrypt url
* Encrypts and decrypts url
* Usage example: - 'index.php?A='.encrypt_url("somedata")
*                - decrypt_url($GET['A'])
*/
function encrypt_url($string) {


        $key = "123abc"; //preset key to use on all encrypt and decrypts.
        $result = '';
   for($i=0; $i<strlen($string); $i++) {
     $char = substr($string, $i, 1);
     $keychar = substr($key, ($i % strlen($key))-1, 1);
     $char = chr(ord($char)+ord($keychar));
     $result.=$char;
   }
   return urlencode(base64_encode($result));
}


$publish = array('method'=> 'feedStory', 
    	  	         'content' => array( 'feed' => $feed, 
                     		             'next' => $appCanvasUrl.'inventory.php?aid='.$_POST[arms_ID].'&prc='.encrypt_url($_POST[arms_Price]).'&amt='.encrypt_url($_POST[arms_amount]).'&action=buyarms'));

 

 

and then in a file that a include file of page the code above it from

 

/**
* Encrypt/decrypt url
* Encrypts and decrypts url
* Usage example: - 'index.php?A='.encrypt_url("somedata")
*                - decrypt_url($GET['A'])
*/
function encrypt_url($string) {


        $key = "123abc"; //preset key to use on all encrypt and decrypts.
        $result = '';
   for($i=0; $i<strlen($string); $i++) {
     $char = substr($string, $i, 1);
     $keychar = substr($key, ($i % strlen($key))-1, 1);
     $char = chr(ord($char)+ord($keychar));
     $result.=$char;
   }
   return urlencode(base64_encode($result));
}



//======================================================
// Update Arms Log
//======================================================
if( !empty($_GET[action]) AND $_GET[action]=="buyarms" ) {
$str = add_arms( $user, $_GET[aid], decrypt_url($_GET[prc]), decrypt_url($_GET[amt]) );
}


if( !empty($_GET[action]) AND $_GET[action]=="sellarms" ) {
$str = remove_arms( $user, $_GET[aid], decrypt_url($_GET[prc]), decrypt_url($_GET[amt]) );
}

 

 

 

and this works great the issue is in firefox after lets say i buy something everything updates the url is encrypted but as soon as i click any link to another page or on same page it submits again

 

but its fine in IE

 

the second code is a include file  which is on every page so may be because this

 

any idea or advice please