change the id of the ab delete button so it does not conflict with the delete button in the mail 3-pane. This was confusing the custom toolar dialog, causing it to not show the icon.

mail/components/addrbook/content/addressbook.xul

@@ -464,7 +464,7 @@
       <toolbarbutton class="toolbarbutton-1" id="button-editcard" label="&editButton.label;" tooltiptext="&editButton.tooltip;" oncommand="goDoCommand('button_edit');"/>
       <toolbarbutton class="toolbarbutton-1" id="button-newmessage" label="&newmsgButton.label;" tooltiptext="&newmsgButton.tooltip;" oncommand="AbNewMessage();"/>
       <toolbarbutton class="toolbarbutton-1" id="button-newim" label="&newIM.label;" tooltiptext="&newIM.tooltip;" oncommand="AbIMSelected();"/>
-      <toolbarbutton class="toolbarbutton-1" id="button-delete" observes="button_delete" label="&deleteButton.label;" tooltiptext="&deleteButton.tooltip;" oncommand="goDoCommand('button_delete');"/>
+      <toolbarbutton class="toolbarbutton-1" id="button-abdelete" observes="button_delete" label="&deleteButton.label;" tooltiptext="&deleteButton.tooltip;" oncommand="goDoCommand('button_delete');"/>
 
       <toolbaritem id="throbber-box" align="center" pack="center">
         <button id="navigator-throbber" oncommand="loadThrobberUrl('addressbook.throbber.url')" tooltiptext="&throbber.tooltip;">
@@ -478,7 +478,7 @@
            fullscreentoolbar="true" mode="full"
            customizable="true"
            context="toolbar-context-menu"
-           defaultset="button-newcard,button-newlist,space,button-editcard,button-newmessage,button-newim,button-delete,spring,throbber-box">
+           defaultset="button-newcard,button-newlist,space,button-editcard,button-newmessage,button-newim,button-abdelete,spring,throbber-box">
    </toolbar>
    <toolbarset id="customToolbars" context="toolbar-context-menu"/>
   </toolbox>

mail/components/addrbook/skin/addressbook.css

@@ -132,16 +132,16 @@ toolbar[mode="text"] .toolbarbutton-text {
  -moz-image-region: rect(60px 150px 90px 120px) !important;
 } 
 
-#button-delete {
+#button-abdelete {
   list-style-image: url("chrome://messenger/skin/addressbook/icons/addressbook-toolbar.png");
   -moz-image-region: rect(0px 180px 30px 150px);
 }
 
-#button-delete:hover {
+#button-abdelete:hover {
   -moz-image-region: rect(30px 180px 60px 150px);
 } 
 
-#button-delete[disabled] {
+#button-abdelete[disabled] {
   -moz-image-region: rect(60px 180px 90px 150px) !important;
 }
 
@@ -216,16 +216,16 @@ toolbar[iconsize="small"] #button-newim[disabled] {
   -moz-image-region: rect(40px 100px 60px 80px) !important;
 } 
 
-toolbar[iconsize="small"] #button-delete {
+toolbar[iconsize="small"] #button-abdelete {
    list-style-image: url("chrome://messenger/skin/addressbook/icons/addressbook-toolbar-small.png");
   -moz-image-region: rect(0px 120px 20px 100px);
 }
 
-toolbar[iconsize="small"] #button-delete:hover {
+toolbar[iconsize="small"] #button-abdelete:hover {
   -moz-image-region: rect(20px 120px 40px 100px);
 } 
 
-toolbar[iconsize="small"] #button-delete[disabled] {
+toolbar[iconsize="small"] #button-abdelete[disabled] {
   -moz-image-region: rect(40px 120px 60px 100px) !important;
 }