add auto completion for about urls (#595)

eg: about:config, about:addons etc

Author: amzyang

common/content/completion.js

@@ -717,6 +717,17 @@ const Completion = Module("completion", {
         if (options.urlseparator)
             skip = context.filter.match("^.*" + options.urlseparator); // start after the last 'urlseparator'
 
+        if (/^about:/.test(context.filter))
+            context.fork("about", 6, this, function fork_(context) {
+                context.title = ["about:"];
+                context.generate = function generate_() {
+                    return Object.keys(Cc).filter(k => k.startsWith(services.ABOUT))
+                        .map(k => [k.substr(services.ABOUT.length),
+                            ""]);
+                };
+            });
+
+
         if (skip)
             context.advance(skip[0].length);
 

common/content/services.js

@@ -11,6 +11,7 @@
  * @constructor
  */
 const Services = Module("services", {
+    ABOUT: "@mozilla.org/network/protocol/about;1?what=",
     init: function () {
         this.classes = {};
         this.jsm = window.Services;