@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

/* Use [label*="whatever"] if your keyword occurs anywhere in the title. You can replace * with ^ or $ if the title 'starts with' or 'ends with' the keyword you supply.
You can remove [label="folder name"] to apply the style on all live bookmarks */

.bookmark-item[label="folder name"][livemark="true"] menuitem[label*="keyword/phrase"] > label {
  font-weight: bold !important;
  color: red !important;
}