I have already explained this in the context of Gmail, but I thought we should make it more explicit.

If you go on Music Oricon Japanese Web site with Firefox Android with about:config?filter=prefixes.webkit set to false, you will see massive breakages, including this navigation bar:

There are a couple issues including flexbox, but let's ignore it for the moment and let's focus on background-image issues. The markup is simple.

<ul class="btn-navi">
        <li class="current"><a href="http://music.oricon.co.jp/?&clt=WW5retn8C31gDygq5DOAPvc732o8EWMcQAtlkTOLQNcOUlh72xokjWq9tkN7-TQX24EuyA~~">J-POPspan>a>span>li>
        <li><a href="http://music-world.oricon.co.jp/?&clt=WW5retn8C31gDygq5DOAPvc732o8EWMcQAtlkTOLQNcOUlh72xokjWq9tkN7-TQX24EuyA~~">

http://www.otsukare.info/2016/05/25/howto-fix-css-border-image