Bug: No backtrace on exceptions under Firefox about opal HOT 6 CLOSED

diff --git a/opal/corelib/error.rb b/opal/corelib/error.rb
index da74c1cea..9d6c24eb1 100644
--- a/opal/corelib/error.rb
+++ b/opal/corelib/error.rb
@@ -11,6 +11,10 @@ class ::Exception < `Error`
       error.name    = self.$$name;
       error.message = message;
       error.cause   = #{$!};
+
+      // A bug in Firefox would not set a stack for non-direct descendants of Error
+      error.stack   = (new Error).stack;
+
       Opal.send(error, error.$initialize, args);
 
       // Error.captureStackTrace() will use .name and .toString to build the

diff --git a/opal/corelib/runtime.js b/opal/corelib/runtime.js
index 11671ac13..9dfda69e1 100644
--- a/opal/corelib/runtime.js
+++ b/opal/corelib/runtime.js
@@ -567,7 +567,7 @@
   // @return new [Class]  or existing ruby class
   //
   function $allocate_class(name, superclass, singleton) {
-    var klass;
+    var klass, super_constructor;
 
     if (superclass != null && superclass.$$bridge) {
       // Inheritance from bridged classes requires
@@ -581,7 +581,9 @@
         return self;
       }
     } else {
-      klass = function(){};
+      klass = function() {
+        if (superclass) superclass.$$constructor(this, arguments);
+      };
     }
 
     if (name && name !== nil) {

diff --git a/opal/corelib/runtime.js b/opal/corelib/runtime.js
index 11671ac13..301139d42 100644
--- a/opal/corelib/runtime.js
+++ b/opal/corelib/runtime.js
@@ -538,6 +538,13 @@
   Opal.$$$ = Opal.const_get_qualified;
   Opal.$r = Opal.const_get_relative_factory;
 
+  function descends_from_bridged_class(klass) {
+    if (klass == null) return false;
+    if (klass.$$bridge) return klass;
+    if (klass.$$super) return descends_from_bridged_class(klass.$$super);
+    return false;
+  }
+
   // Modules & Classes
   // -----------------
 
@@ -567,14 +574,14 @@
   // @return new [Class]  or existing ruby class
   //
   function $allocate_class(name, superclass, singleton) {
-    var klass;
+    var klass, bridged_descendant;
 
-    if (superclass != null && superclass.$$bridge) {
+    if (bridged_descendant = descends_from_bridged_class(superclass)) {
       // Inheritance from bridged classes requires
       // calling original JS constructors
       klass = function() {
         var args = $slice(arguments),
-            self = new ($bind.apply(superclass.$$constructor, [null].concat(args)))();
+            self = new ($bind.apply(bridged_descendant.$$constructor, [null].concat(args)))();
 
         // and replacing a __proto__ manually
         $set_proto(self, klass.$$prototype);