The link to the themes is in fact not in the XUL namespace... change those

rules to match all namespaces, just in case.  Bug 214463, r=mkaply, sr=rbs

themes/classic/communicator/prefpanels.css

@@ -40,22 +40,20 @@
    ====================================================================== */
 
 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
-@namespace html url("http://www.w3.org/1999/xhtml");
-
 /* ::::: Themes ::::: */
 
 #skinsTree {
   height: 80px;
 }
 
-.themesLink {
+*|*.themesLink {
   margin-left: 5px;
   text-decoration: underline;
   color: blue;
   cursor: pointer;
 }
 
-.themesLink:active {
+*|*.themesLink:active {
   color: red;
 }
 

themes/modern/communicator/prefpanels.css

@@ -40,22 +40,20 @@
    ====================================================================== */
 
 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
-@namespace html url("http://www.w3.org/1999/xhtml");
-
 /* ::::: Themes ::::: */
 
 #skinsTree {
   height: 80px;
 }
 
-.themesLink {
+*|*.themesLink {
   margin-left: 5px;
   text-decoration: underline;
   color: blue;
   cursor: pointer;
 }
 
-.themesLink:active {
+*|*.themesLink:active {
   color: red;
 }