title: Input controls overflowing flex container in Firefox
body: <p>I'm having issues on Firefox (fine in Chrome) with a flexbox input group - the select input is pushing the text input out of the container.</p>
  
  <p>I've extracted some of the markup and replicated the relevant styling below:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.column.names {
    width: 48%;
    float: left;
  }
  select {
    min-width: 6em;
    align-items: center;
    justify-content: center;
    width: 7em;
  }
  input {
    width: 100%;
  }
  .input_group {
    display: flex;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class='column names'&gt;
  
    &lt;div&gt;
      &lt;label for="user_name"&gt;Name&lt;/label&gt;
      &lt;div&gt;
        &lt;div class='input_group'&gt;
          &lt;select name="user[title]" id="user_title"&gt;
            &lt;option value=""&gt;&lt;/option&gt;
            &lt;option selected="selected" value="Mr"&gt;Mr&lt;/option&gt;
            &lt;option value="Mrs"&gt;Mrs&lt;/option&gt;
            &lt;option value="Other"&gt;Other&lt;/option&gt;
          &lt;/select&gt;
          &lt;input maxlength="255" size="255" type="text" name="user[name]" id="user_name" /&gt;
        &lt;/div&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  
    &lt;div&gt;
      &lt;label for="user_company"&gt;Company&lt;/label&gt;
      &lt;div&gt;
        &lt;input maxlength="255" size="255" type="text" value="" name="user[company]" id="user_company" /&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://jsfiddle.net/j9s0fk8c/" rel="noreferrer">https://jsfiddle.net/j9s0fk8c/</a></p>
  
  <p>To clarify, the Name select + input box combined should be the same width as the Company input box.</p>
  
  <p>Again this has been fine in Chrome but for some reason flexbox is giving us no end of issues in Firefox (this is just one in a long line of weird issues we've had to deal with)</p>