modify date format on stackoverflow and stackexchange sites using userContent.css for Firefox

.mozilla_firefox_$profile_userContent.css

/*
 * Please share improvements here or on StackOverflow and add a link here.
 * Please upvote https://meta.stackoverflow.com/questions/288674/custom-date-format/385090#385090 if you agree that
 * users should have a choice of date format available.
 *
 *  - see https://developer.mozilla.org/en-US/docs/Web/CSS/@document
 *  - https://www.regextester.com/ may be useful too, but careful of the double escaping!
 * keywords: date format, date display, stackoverflow, stackexchange, css, script
 */

/* this doesn't work ->  @-moz-document domain(stackoverflow.com) domain(stackexchange.com) */
@-moz-document regexp('.*(askubuntu|stackoverflow|stackexchange)\\.com/?.*')
{
span.relativetime { overflow: hidden; color:#fff; }
span.relativetime::before { color:#333;
  content: attr(title) ' ';
  width: 50%;
  display:inline-block;
  height:1.1em; overflow: hidden;
  white-space: pre-wrap;
  }

span.relativetime-clean { color:#fff; }
span.relativetime-clean::before { color:#333;
  font-weight: bold;
  content: ' ' attr(title) ' ';
  display:inline-block;
  }
}

If you make improvements please post them back in a comment.