Fix some bugs.

common/content/commandline.js

@@ -659,6 +659,9 @@ const CommandLine = Module("commandline", {
      *          the MOW.
      */
     echo: function echo(str, highlightGroup, flags) {
+        if (String(str) == "undefined")
+            util.dumpStack();
+
         // dactyl.echo uses different order of flags as it omits the highlight group, change commandline.echo argument order? --mst
         if (this._silent)
             return;