Why does Firefox delete part of my CSS selector despite that it actually matches something in the HTML when testing it in the web inspector?

Question

I have this HTML:

<div class="fieldset" tabindex="0">
  <div class="field configurable required">
    <label class="label" for="attribute140">
      <span>Property</span>
    </label>
    <div class="control">
      <select name="super_attribute[140]" data-selector="super_attribute[140]" data-validate="{required:true}" id="attribute140" class="super-attribute-select" data-ddg-inputtype="unknown" aria-required="true">
        <option value="">Select an option...</option>
        <option value="86">XXL</option>
      </select>
    </div>
  </div>
</div>

I want to target the second option (XXL) with a CSS selector. .super-attribute-select option finds both options. I am not good at this so I experimented in the inspector panel in Firefox's web inspector and therefore tried .super-attribute-select option:nth-of-type(2) but when I entered this Firefox displayed a pop-up menu with a "suggested" (?) CSS selector and as soon as I press enter the :nth-of-type(2) part of the expression is deleted.

The result of the deletion of this part is that my selector matches two elements.

Is my CSS selector erroneous (I have tried with 0 and 1 instead of 2)? Why does Firefox not accept my CSS selector/deletes the last part of it? How do I test this, the full, CSS selector in the inspector panel of Firefox's web inspector? Even if my CSS selector is broken and matches nothing, an empty result is still useful when learning this.

Answer 1

Your selector is correct. This is a bug in the Inspector search that just got filed yesterday.

It also occurs for other pseudo-classes like the recently introduced :has().

As a workaround, you may use your selector in the Web Console's command line instead and wrap it in a $(), i.e. $('.super-attribute-select option:nth-of-type(2)'). If you execute that, the console outputs the element it matches. Then you can click the little target icon besides it to switch to the Inspector and select it there.