如果内容长度更长，则下拉选项应在左侧浮动

Question

我遇到HTML下拉列表（select标签）的问题，当我尝试在Firefox中打开网站时，其选项显示在浏览器窗口之外，但在其他浏览器中工作正常。

我希望如果内容长度太大，那么下拉列表应该向左侧弹出，否则它应该是（默认）右侧。

:root .css3-metro-dropdown option,
:root .css3-metro-dropdown:after,
:root .css3-metro-dropdown::after,
:root .css3-metro-dropdown select {
  color: #fff;
}

:root .css3-metro-dropdown select,
:root .css3-metro-dropdown:after,
:root .css3-metro-dropdown::after {
  display: block;
  background: #78ba00;
}

:root .css3-metro-dropdown select,
:root .css3-metro-dropdown option {
  padding: 8px;
}

:root .css3-metro-dropdown {
  position: relative;
  display: inline-block;
  border: 0;
}

:root .css3-metro-dropdown::after {
  content: "\25bc";
  position: absolute;
  top: 0;
  right: 0;
  display: block;
  width: 32px;
  font-size: 12px;
  line-height: 34px;
  text-align: center;
  -webkit-pointer-events: none;
  -moz-pointer-events: none;
  pointer-events: none;
}

:root .css3-metro-dropdown select {
  height: 34px;
  border: 0;
  vertical-align: middle;
  font: normal 12px/14px"Segoe UI", Arial, Helvetica, Sans-serif;
  outline: 0 none;
}

:root .css3-metro-dropdown option {
  background: #fff;
  color: #333;
}

<span class="css3-metro-dropdown">
   <select name="dropdown-1">
     <option value="0">Client-side Languages</option>
     <option value="1">JavaScript</option>        
     <option value="2">CSS3</option>
     <option value="3">HTML5</option>
   </select>
</span>