CSS flexbox width 100% Firefox

I'm having an issue with this scenario in Firefox. #pager takes the width of its children. However, in Chrome, it takes the width of its parent. How can I make #item-list respect the width of its parent in Firefox?

take a look! https://jsfiddle.net/owmpatbh/2/

HTML:

<div id="wrapper">
  <div id="sidebar"></div>
    <div id="main">
      <div id="content">
        <p id="stuff">blahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblah</p>            
      </div>
      <div id="pager">
          <div id="item-list">
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
              <div class="item"></div>
          </div>
      </div>
   </div>
</div>

CSS:

#wrapper {


 display: flex;
  width: 100%;
  height: 100%;
}

#sidebar {
  overflow: auto;
  flex: 0.25;
  border:3px solid green;
  min-height: 200px; 
}

#main {
  display: flex;
  flex: .75;
  flex-direction: column;
  border:3px solid orange;
}

#content {
  position: relative;
  width: 100%;
  flex: 0.85;
  border: 3px solid blue;
}

#pager {
  display: flex;
  position: relative;
  width: 100%;
  background-color: #fff;
  border: 3px solid pink;
  flex: 0.15;
}

#item-list {
  border: 1px solid black;
  width: 100%;
  overflow-x: scroll;
  overflow-y: hidden;
  white-space: nowrap;
}

.item {
    display: inline-block;
    padding: 5px;
    width: 200px;
    height: 200px;
    background-color: red;
}

#stuff {
    height: 200px;
}

*{
    margin: 3px;
}