Bug 414443: New addons UI cancel icon doesn't always change back to magnifying glass icon. r=robstrong

toolkit/mozapps/extensions/content/extensions.xml

@@ -902,8 +902,14 @@
         document.getAnonymousElementByAttribute(this, "class", "searchbox-cancel");
       </field>
 
-      <property name="value" onget="return this.textbox.value"
-                             onset="this.textbox.value = val"/>
+      <property name="value" onget="return this.textbox.value">
+        <setter>
+          this.textbox.value = val;
+          this.setAttribute("value", val);
+          this._cancelButton.hidden = !val;
+          this._searchButton.hidden = !!val;
+        </setter>
+      </property>
 
       <property name="disabled" onget="return this.textbox.disabled">
         <setter>