Suggestengines only using visible search engines:

* Non-visible, or deleted search engines are not exposed
  in the UI, and as far as the user is concerned they do
  not exist.
* The default search engines (or other deleted ones) may
  still be stored (search.json etc).
* With this in mind, suggestengines should respect the
  ability to delete (hide) engines, and only show/use
  visible search engines.

Author: timss

common/content/commandline.js

@@ -1617,7 +1617,7 @@ const CommandLine = Module("commandline", {
              "stringlist", "google",
              {
                  completer: function completer(value) {
-                     let engines = services.get("search").getEngines({})
+                     let engines = services.get("search").getVisibleEngines({})
                                            .filter(function (engine) engine.supportsResponseType("application/x-suggestions+json"));
 
                      return engines.map(function (engine) [engine.alias, engine.description]);