マウスオーバーするとテキストが動くので　https://github.com/manilarome/blurredfox/blob/master/userChrome.css
.tab-content {justify-content: center !important; align-items: center !important;}
.tab-content::before{content: "" !important; display: -moz-box !important; -moz-box-flex: 1 !important;}