--- a/browser/components/search/content/search.xml
+++ b/browser/components/search/content/search.xml
@@ -1147,16 +1147,19 @@
       <handler event="contextmenu"><![CDATA[
         let target = event.originalTarget;
         // Prevent the context menu from appearing except on the one off buttons.
         if (!target.classList.contains("searchbar-engine-one-off-item") ||
             target.classList.contains("dummy")) {
           event.preventDefault();
           return;
         }
+        document.getAnonymousElementByAttribute(this, "anonid", "search-one-offs-context-set-default")
+                .setAttribute("disabled", target.engine == Services.search.currentEngine);
+
         this._contextEngine = target.engine;
       ]]></handler>
 
       <handler event="popupshowing"><![CDATA[
         // First handle deciding if we are showing the reduced version of the
         // popup containing only the preferences button. We do this if the
         // glass icon has been clicked if the text field is empty.
         let searchbar = document.getElementById("searchbar");