use the triangle for mail ui twisty and the +/- for advanced options.

mail/base/skin/messageHeader.css

@@ -166,11 +166,11 @@ description[selectable="true"]:focus > descriptionitem[selected="true"]
 
 .addresstwisty {
   margin: 2px;
-  list-style-image: url("chrome://global/skin/tree/twisty-clsd.gif");
+  list-style-image: url("chrome://messenger/skin/icons/twisty-clsd.gif");
 }
 
 .addresstwisty[open] {
-  list-style-image: url("chrome://global/skin/tree/twisty-open.gif");
+  list-style-image: url("chrome://messenger/skin/icons/twisty-open.gif");
 }
 
 /* ::::: view expand and collapse twisties  ::::: */
@@ -181,11 +181,11 @@ description[selectable="true"]:focus > descriptionitem[selected="true"]
 }
 
 .expandHeaderViewButton {
-  list-style-image: url("chrome://global/skin/tree/twisty-open.gif");
+  list-style-image: url("chrome://messenger/skin/icons/twisty-open.gif");
 }
 
 .collapsedHeaderViewButton  {
-  list-style-image: url("chrome://global/skin/tree/twisty-clsd.gif");
+  list-style-image: url("chrome://messenger/skin/icons/twisty-clsd.gif");
 }
 
 /* ::::: collapsed view styles ::::: */

mail/base/skin/tree.css

@@ -265,12 +265,12 @@ treechildren::-moz-tree-column(insertafter) {
 treechildren::-moz-tree-twisty {
   padding-right: 2px;
   width: 10px; /* The image's width is 9 pixels */
-  list-style-image: url("chrome://global/skin/tree/twisty-clsd.gif");
+  list-style-image: url("chrome://messenger/skin/icons/twisty-clsd.gif");
 }
 
 treechildren::-moz-tree-twisty(open) {
   width: 10px; /* The image's width is 9 pixels */
-  list-style-image: url("chrome://global/skin/tree/twisty-open.gif");
+  list-style-image: url("chrome://messenger/skin/icons/twisty-open.gif");
 }
 
 treechildren::-moz-tree-indentation {