Edit: This question is already different from the one that was voted duplicate, How to remove the arrow from a select element in Firefox. That question was referenced in the question from the start - before trying to get your daily limit of close votes, please read the question.
I'm using the HtmlService of Google Apps Script to display an HTML form, including jQuery and javascript. Using the recommended stylesheet for Google Doc add-ons, this is how a select box appears in Chrome:
Here's the same thing, in Firefox. Note the extra superimposed arrow.
How can I get rid of that overlay in Firefox?
I've tried the techniques described in How to remove the arrow from a select element in Firefox, but the accepted and highest voted answers stopped working in more recent versions of FF, and didn't work for me. Other solutions involving overflowing the select and hiding the overflow with an enclosing div are interesting, but since they also eliminate the desired "up/down" arrows, they aren't acceptable for this application.
HTML
<div class="block form-group">
<label for="my-selection">Select an option:</label>
<select class="width-100" id="my-selection">
<option value="Option 1"></option>
<option value="Option 2"></option>
<option value="Option 3"></option>
</select>
</div>
CSS
<link rel="stylesheet" href="https://ssl.gstatic.com/docs/script/css/add-ons.css">
<!-- The CSS package above applies Google styling to buttons and other elements. -->
<style>
.width-100 {
width: 100%;
}
select {
height: 31px;
}
</style>