titlebar of box can "stick" out of titlebar in firefox - documentation problem?

[graf0]

Hi,

we have following code:

<div class="box">
  <div class="block titlebar">
    <strong>pike</strong>
  </div>
  <p>
    node is git
    <span class="float:right">
      <a href="#">ssh</a> |
      <a href="/systems/1/nodes/2">→ goto</a>
    </span>
  </p>
</div>

This is how it looks on Edge - as it should:

And this is how it looks on Firefox:

Notice how letter "p" goes just a little bit out of titlebar. There is also more shadow under it.

[graf0]

After adding to head of my page this (copied from missing.style):

<link rel="stylesheet" href="https://fonts.bunny.net/css?family=source-sans-3:400,700|m-plus-code-latin:400,700">

Now it display box titlebar correctly in all browsers.
It seems to be documentation problem - maybe you should add this line to installation instructions?