Backing myself out. mscott had already landed a different and more correct fix for this problem elsewhere in the tree.

mail/locales/en-US/chrome/global/charset.dtd

@@ -1,20 +0,0 @@
-<!ENTITY charsetMenu.label        "Character Encoding">
-<!ENTITY charsetMenu.accesskey        "C">
-<!ENTITY charsetMenuAutodet.label     "Auto-Detect">
-<!ENTITY charsetMenuAutodet.accesskey     "a">
-<!ENTITY charsetMenuMore.label        "More">
-<!ENTITY charsetMenuMore.accesskey        "m">
-<!ENTITY charsetMenuMore1.label       "West European">
-<!ENTITY charsetMenuMore1.accesskey       "w">
-<!ENTITY charsetMenuMore2.label       "East European">
-<!ENTITY charsetMenuMore2.accesskey       "E">
-<!ENTITY charsetMenuMore3.label       "East Asian">
-<!ENTITY charsetMenuMore3.accesskey       "A">
-<!ENTITY charsetMenuMore4.label       "SE &amp; SW Asian">
-<!ENTITY charsetMenuMore4.accesskey       "S">
-<!ENTITY charsetMenuMore5.label       "Middle Eastern">
-<!ENTITY charsetMenuMore5.accesskey       "M">
-<!ENTITY charsetMenuUnicode.label       "Unicode">
-<!ENTITY charsetMenuUnicode.accesskey       "U">
-<!ENTITY charsetCustomize.label       "Customize...">
-<!ENTITY charsetCustomize.accesskey       "c">

mail/locales/jar.mn

@@ -24,7 +24,6 @@
   locale/@AB_CD@/messenger/addressbook/abContactsPanel.dtd (@AB_CD@/chrome/messenger/addressbook/abContactsPanel.dtd)
 + locale/@AB_CD@/messenger-mapi/mapi.properties            (@AB_CD@/chrome/messenger-mapi/mapi.properties)
 + locale/@AB_CD@/communicator/utilityOverlay.dtd           (@AB_CD@/chrome/communicator/utilityOverlay.dtd)
-+ locale/@AB_CD@/global/charset.dtd                        (@AB_CD@/chrome/global/charset.dtd)
 + locale/@AB_CD@/global/brand.properties                   (@AB_CD@/chrome/global/brand.properties)
 * locale/@AB_CD@/global/brand.dtd                          (@AB_CD@/chrome/global/brand.dtd)