<select id="dynamic_select_company"> // On change the selected option is triggered
<?php
  $countcompany = $pdo->prepare( $filterkomplex1 );
  $countcompany->execute(); ?>
<option value="Browse.php" selected>Choose Company...</option>

<?php while($showcompany = $countcompany->fetch()) {?>
<option
<?php
  if ($_GET['Company'] == $showcompany['Company']) { ?> selected="true" <?php }; ?>
    value="<?php echo $furl ?>&Company=<?php echo $showcompany['Company']?>">  // i know this will append infinity GET_Parameters
<?php echo $showcompany['Company']?> (<?php echo $showcompany['anzahl']?>) </option>
<?php };?>
</select>

<button>Delete part of string where GET-Parameter is &Company=XYZ</button>

<select id="dynamic_select_line"> ...
<button>Delete part of string where GET-Parameter is &Line=XYZ</button>
<select id="dynamic_select_group"> ...
<button>Delete part of string where GET-Parameter is &Group=XYZ</button>
<select id="dynamic_select_year">  ...
<button>Delete part of string where GET-Parameter is &Year=XYZ</button>