Serialize :loadplugins command so that options and commands defined by plugins work properly by default.

common/content/options.js

@@ -391,6 +391,9 @@ const Option = Class("Option", {
     },
 
     parseRegexp: function (value, result, flags) {
+        if (isArray(flags)) // Called by map
+            result = flags = undefined;
+
         let [, bang, val] = /^(!?)(.*)/.exec(value);
         let re = RegExp(Option.dequote(val), flags);
         re.bang = bang;