title: Bootstrap 4 Card Flex Width is not working correctly on Firefox
body: <p>I have a problem trying to make a webpage with bootstrap 4 and flex. I am using Bootstrap cards with certain width. I see that this works fine in Google Chrome and Opera but appears to not work in Firefox.
  Here is my code:</p>
  
  <pre><code>    &lt;div class="row auxAltura2"&gt;
      &lt;div class="col"&gt;
          &lt;div class="card"&gt;
              &lt;div class="card-header colorPlataforma"&gt;
                  Tags
              &lt;/div&gt;
              &lt;div id="moduloTags" class="card-body"&gt;
                  ...
  
              &lt;/div&gt;
  
          &lt;/div&gt;
      &lt;/div&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>And now here is my css:</p>
  
  <pre><code>   .auxAltura2{height:250px}
      .card-header{
          display: flex;
          flex: 1 0 30px;
          align-items: center;
          font-size:17px;
      }
  </code></pre>
  
  <p>Image card on firefox:</p>
  
  <p><a href="https://i.stack.imgur.com/rdHF3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rdHF3.png" alt="enter image description here"></a></p>
  
  <p>And this is image from card on Opera:</p>
  
  <p><a href="https://i.stack.imgur.com/MNg89.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MNg89.png" alt="enter image description here"></a></p>
  
  <p>You can see the difference between the 2 browsers. Is a bug? 
  Glad if you can help me. Thanks for all. </p>