Table inside inline-block Firefox issue

HTML

<div style="float: left; width: -moz-fit-content;">
  <div id="a">
    <div id="b">b</div>
    <div id="c">c1 c2</div>
  </div>
</div>

CSS

#a {
  display: inline-block;
  width: 100%;
  overflow: hidden;
  vertical-align: top;
  white-space: nowrap;
}

#b {
  float: left;
  background: lightgray;
}

#c {
  overflow: hidden;
  background: gray;
  width: -moz-fit-content;
}