Fix access key for Switch Theme button...the old one, a, no longer applies.

xpfe/components/prefwindow/resources/locale/en-US/pref-themes.dtd

@@ -6,7 +6,7 @@
 <!ENTITY  installedThemes.label   "Installed themes:">
 
 <!ENTITY  selectSkin.label        "Switch Theme">
-<!ENTITY  selectSkin.accesskey    "a">
+<!ENTITY  selectSkin.accesskey    "s">
 
 <!ENTITY  installSkin.label       "Install Theme...">
 <!ENTITY  installSkin.accesskey   "i">