diff --git a/js/src/jsfun.cpp b/js/src/jsfun.cpp
index 048063435c97..2b5fe5a14eda 100644
--- a/js/src/jsfun.cpp
+++ b/js/src/jsfun.cpp
@@ -1268,7 +1268,7 @@ js_CloneFunctionObject(JSContext *cx, HandleFunction fun, HandleObject parent,
         clone->initializeExtended();
     }
 
-    if (cx->compartment == fun->compartment()) {
+    if (cx->compartment == fun->compartment() && !types::UseNewTypeForClone(fun)) {
         /*
          * We can use the same type as the original function provided that (a)
          * its prototype is correct, and (b) its type is not a singleton. The
@@ -1279,6 +1279,9 @@ js_CloneFunctionObject(JSContext *cx, HandleFunction fun, HandleObject parent,
         if (fun->getProto() == proto && !fun->hasSingletonType())
             clone->setType(fun->type());
     } else {
+        if (!clone->setSingletonType(cx))
+            return NULL;
+
         /*
          * Across compartments we have to clone the script for interpreted
          * functions. Cross-compartment cloning only happens via JSAPI
@@ -1289,22 +1292,24 @@ js_CloneFunctionObject(JSContext *cx, HandleFunction fun, HandleObject parent,
             RootedScript script(cx, clone->script());
             JS_ASSERT(script);
             JS_ASSERT(script->compartment() == fun->compartment());
-            JS_ASSERT(script->compartment() != cx->compartment);
-            JS_ASSERT(!script->enclosingStaticScope());
+            JS_ASSERT_IF(script->compartment() != cx->compartment,
+                         !script->enclosingStaticScope() && !script->compileAndGo);
+
+            RootedObject scope(cx, script->enclosingStaticScope());
 
             clone->mutableScript().init(NULL);
 
-            JSScript *cscript = CloneScript(cx, NullPtr(), clone, script);
+            JSScript *cscript = CloneScript(cx, scope, clone, script);
             if (!cscript)
                 return NULL;
 
             clone->setScript(cscript);
             cscript->setFunction(clone);
-            if (!clone->setTypeForScriptedFunction(cx))
-                return NULL;
+
+            GlobalObject *global = script->compileAndGo ? &script->global() : NULL;
 
             js_CallNewScriptHook(cx, clone->script(), clone);
-            Debugger::onNewScript(cx, clone->script(), NULL);
+            Debugger::onNewScript(cx, clone->script(), global);
         }
     }
     return clone;
diff --git a/js/src/jsinfer.cpp b/js/src/jsinfer.cpp
index b587ccb35769..ce3f221df968 100644
--- a/js/src/jsinfer.cpp
+++ b/js/src/jsinfer.cpp
@@ -3629,7 +3629,7 @@ ScriptAnalysis::analyzeTypesBytecode(JSContext *cx, unsigned offset,
             res = &pushed[0];
 
         if (res) {
-            if (script->hasGlobal())
+            if (script->hasGlobal() && !UseNewTypeForClone(obj->toFunction()))
                 res->addType(cx, Type::ObjectType(obj));
             else
                 res->addType(cx, Type::UnknownType());
@@ -3926,12 +3926,14 @@ ScriptAnalysis::analyzeTypesBytecode(JSContext *cx, unsigned offset,
         pushed[0].addType(cx, Type::UnknownType());
         break;
 
-      case JSOP_CALLEE:
-        if (script->hasGlobal())
-            pushed[0].addType(cx, Type::ObjectType(script->function()));
+      case JSOP_CALLEE: {
+        JSFunction *fun = script->function();
+        if (script->hasGlobal() && !UseNewTypeForClone(fun))
+            pushed[0].addType(cx, Type::ObjectType(fun));
         else
             pushed[0].addType(cx, Type::UnknownType());
         break;
+      }
 
       default:
         /* Display fine-grained debug information first */
@@ -5040,6 +5042,11 @@ JSFunction::setTypeForScriptedFunction(JSContext *cx, bool singleton)
     if (singleton) {
         if (!setSingletonType(cx))
             return false;
+    } else if (UseNewTypeForClone(this)) {
+        /*
+         * Leave the default unknown-properties type for the function, it
+         * should not be used by scripts or appear in type sets.
+         */
     } else {
         RootedFunction self(cx, this);
 
diff --git a/js/src/jsinferinlines.h b/js/src/jsinferinlines.h
index 98c1b6ad6e93..b7bbd9293f20 100644
--- a/js/src/jsinferinlines.h
+++ b/js/src/jsinferinlines.h
@@ -489,6 +489,66 @@ UseNewTypeAtEntry(JSContext *cx, StackFrame *fp)
            UseNewType(cx, fp->prev()->script(), fp->prevpc());
 }
 
+inline bool
+UseNewTypeForClone(JSFunction *fun)
+{
+    if (fun->hasSingletonType() || !fun->isInterpreted())
+        return false;
+
+    /*
+     * When a function is being used as a wrapper for another function, it
+     * improves precision greatly to distinguish between different instances of
+     * the wrapper; otherwise we will conflate much of the information about
+     * the wrapped functions.
+     *
+     * An important example is the Class.create function at the core of the
+     * Prototype.js library, which looks like:
+     *
+     * var Class = {
+     *   create: function() {
+     *     return function() {
+     *       this.initialize.apply(this, arguments);
+     *     }
+     *   }
+     * };
+     *
+     * Each instance of the innermost function will have a different wrapped
+     * initialize method. We capture this, along with similar cases, by looking
+     * for short scripts which use both .apply and arguments. For such scripts,
+     * whenever creating a new instance of the function we both give that
+     * instance a singleton type and clone the underlying script.
+     */
+
+    JSScript *script = fun->script();
+
+    if (script->length >= 50)
+        return false;
+
+    if (script->hasConsts() ||
+        script->hasObjects() ||
+        script->hasRegexps() ||
+        script->hasClosedArgs() ||
+        script->hasClosedVars())
+    {
+        return false;
+    }
+
+    bool hasArguments = false;
+    bool hasApply = false;
+
+    for (jsbytecode *pc = script->code;
+         pc != script->code + script->length;
+         pc += GetBytecodeLength(pc))
+    {
+        if (*pc == JSOP_ARGUMENTS)
+            hasArguments = true;
+        if (*pc == JSOP_FUNAPPLY)
+            hasApply = true;
+    }
+
+    return hasArguments && hasApply;
+}
+
 /////////////////////////////////////////////////////////////////////
 // Script interface functions
 /////////////////////////////////////////////////////////////////////