keep pre-existing query on dropdown reset and submit

Hi,

I am trying to code the reset to keep values of a sorting query on reset I have basically managed to get it working using the following code

if (isset($_GET['o'])) {
$b = $_GET['o'];
$a = "?o=";
}
function my_qmt_base_url( $base ) {
global $a;
global $b;
return get_bloginfo('url')."/portfolio/".$a .$b;
}
add_filter( 'qmt_base_url', 'my_qmt_base_url');

the return trailingslashit( $base_url ); code in the plugins core.php
is adding a / at the end of the url. I have tried to incorporate
return untrailingslashit( $base_url ); in my code to no avail.

Can anyone help?

Also submitting a new query from the dropdown widget completely clears my sort order string any ideas of which code I have to alter to keep
this query if it exists.

https://www.ads-software.com/extend/plugins/query-multiple-taxonomies/