@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain(addons.mozilla.org) {

  .desc,
  .corner-box > a > img {
    display: none;
  }

  .corner-box:hover > .desc,
  .corner-box:hover > a > img {
    display: block;
  }

}

@-moz-document
    url(https://addons.mozilla.org/firefox/plugins/),
    url(https://addons.mozilla.org/thunderbird/plugins/),
    url(https://addons.mozilla.org/mozilla/plugins/) {

  div.item > h2 {
    border-bottom-width: 0 !important;
  }

  div.item:hover > h2 {
    border-bottom-width: 1px !important;
  }

  div.item > h3,
  div.item > div {
    display: none;
  }

  div.item:hover > h3,
  div.item:hover > div {
    display: block;
  }
}