Edit in JSFiddle

#browser::after{
  content: "不明";
}
@media (-moz-touch-enabled:0), (-moz-touch-enabled:1){ /* https://developer.mozilla.org/en/CSS/Media_queries */
  #browser::after{
    content: "Gecko 1.9.2 (Firefox 3.6) or later";
  }
}
@media (-moz-device-pixel-ratio){ /* https://developer.mozilla.org/en/CSS/Media_queries */
  #browser::after{
    content: "Gecko 2.0 (Firefox 4) or later";
  }
}
@media (-ms-high-contrast: none){ /* http://msdn.microsoft.com/en-us/library/windows/apps/hh453556.aspx */
  #browser::after{
    content: "Internet Explorer 10";
  }
}
@media (-webkit-animation){ /* https://developer.apple.com/library/safari/documentation/AppleApplications/Reference/SafariCSSRef/Articles/OtherStandardCSS3Features.html#//apple_ref/css/rule/@media */
  #browser::after{
    content: "Webkit (Safari or Chrome)";
  }
}

<span id="browser">ブラウザーは？</span>