diff --git a/js/jsd/jsd.h b/js/jsd/jsd.h
index 65418937207..58b54ef7a8f 100644
--- a/js/jsd/jsd.h
+++ b/js/jsd/jsd.h
@@ -340,7 +340,9 @@ extern void JSD_ASSERT_VALID_OBJECT(JSDObject* jsdobj);
 extern JSDContext*
 jsd_DebuggerOnForUser(JSRuntime*         jsrt,
                       JSD_UserCallbacks* callbacks,
-                      void*              user);
+                      void*              user,
+                      JSObject*          scopeobj);
+
 extern JSDContext*
 jsd_DebuggerOn(void);
 
diff --git a/js/jsd/jsd_high.c b/js/jsd/jsd_high.c
index b2e6fc00b3c..512527636d6 100644
--- a/js/jsd/jsd_high.c
+++ b/js/jsd/jsd_high.c
@@ -86,9 +86,11 @@ _validateUserCallbacks(JSD_UserCallbacks* callbacks)
 static JSDContext*
 _newJSDContext(JSRuntime*         jsrt, 
                JSD_UserCallbacks* callbacks, 
-               void*              user)
+               void*              user,
+               JSObject*          scopeobj)
 {
     JSDContext* jsdc = NULL;
+    JSCompartment *compartment;
 
     if( ! jsrt )
         return NULL;
@@ -137,7 +139,11 @@ _newJSDContext(JSRuntime*         jsrt,
 
     JS_BeginRequest(jsdc->dumbContext);
 
+    if( scopeobj )
+        compartment = js_SwitchToObjectCompartment(jsdc->dumbContext, scopeobj);
     jsdc->glob = JS_NewGlobalObject(jsdc->dumbContext, &global_class);
+    if( scopeobj )
+        js_SwitchToCompartment(jsdc->dumbContext, compartment);
     if( ! jsdc->glob )
         goto label_newJSDContext_failure;
 
@@ -194,12 +200,13 @@ _destroyJSDContext(JSDContext* jsdc)
 JSDContext*
 jsd_DebuggerOnForUser(JSRuntime*         jsrt, 
                       JSD_UserCallbacks* callbacks, 
-                      void*              user)
+                      void*              user,
+                      JSObject*          scopeobj)
 {
     JSDContext* jsdc;
     JSContext* iter = NULL;
 
-    jsdc = _newJSDContext(jsrt, callbacks, user);
+    jsdc = _newJSDContext(jsrt, callbacks, user, scopeobj);
     if( ! jsdc )
         return NULL;
 
@@ -226,7 +233,7 @@ jsd_DebuggerOn(void)
 {
     JS_ASSERT(_jsrt);
     JS_ASSERT(_validateUserCallbacks(&_callbacks));
-    return jsd_DebuggerOnForUser(_jsrt, &_callbacks, _user);
+    return jsd_DebuggerOnForUser(_jsrt, &_callbacks, _user, NULL);
 }
 
 void
diff --git a/js/jsd/jsdebug.c b/js/jsd/jsdebug.c
index 5aa4177eeff..173c9d060fe 100644
--- a/js/jsd/jsdebug.c
+++ b/js/jsd/jsdebug.c
@@ -49,7 +49,7 @@ JSD_DebuggerOnForUser(JSRuntime*         jsrt,
                       JSD_UserCallbacks* callbacks,
                       void*              user)
 {
-    return jsd_DebuggerOnForUser(jsrt, callbacks, user);
+    return jsd_DebuggerOnForUser(jsrt, callbacks, user, NULL);
 }
 
 JSD_PUBLIC_API(JSDContext*)
diff --git a/js/jsd/jsdebug.h b/js/jsd/jsdebug.h
index 41eab2a9429..fcdc2e04ee8 100644
--- a/js/jsd/jsdebug.h
+++ b/js/jsd/jsdebug.h
@@ -142,6 +142,16 @@ JSD_DebuggerOnForUser(JSRuntime*         jsrt,
                       JSD_UserCallbacks* callbacks,
                       void*              user);
 
+/*
+ * Startup JSD in an application that uses compartments. Debugger
+ * objects will be allocated in the same compartment as scopeobj.
+ */
+extern JSD_PUBLIC_API(JSDContext*)
+JSD_DebuggerOnForUserWithCompartment(JSRuntime*         jsrt,
+                                     JSD_UserCallbacks* callbacks,
+                                     void*              user,
+                                     JSObject*          scopeobj);
+
 /*
 * Shutdown JSD for this JSDContext
 */
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index fa2c26ebdb3..4a27e11ce3f 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -1185,22 +1185,20 @@ JSAutoCrossCompartmentCall::enter(JSContext *cx, JSObject *target)
     return call != NULL;
 }
 
-JSAutoEnterCompartment::JSAutoEnterCompartment(JSContext *cx,
-                                               JSCompartment *newCompartment)
-  : cx(cx), compartment(cx->compartment)
-{
-    cx->compartment = newCompartment;
-}
-
-JSAutoEnterCompartment::JSAutoEnterCompartment(JSContext *cx, JSObject *target)
-  : cx(cx), compartment(cx->compartment)
-{
-    cx->compartment = target->getCompartment(cx);
-}
-
-JSAutoEnterCompartment::~JSAutoEnterCompartment()
+JS_FRIEND_API(JSCompartment *)
+js_SwitchToCompartment(JSContext *cx, JSCompartment *compartment)
 {
+    JSCompartment *c = cx->compartment;
     cx->compartment = compartment;
+    return c;
+}
+
+JS_FRIEND_API(JSCompartment *)
+js_SwitchToObjectCompartment(JSContext *cx, JSObject *obj)
+{
+    JSCompartment *c = cx->compartment;
+    cx->compartment = obj->getCompartment(cx);
+    return c;
 }
 
 JS_PUBLIC_API(void *)
@@ -1245,7 +1243,8 @@ JS_SetGlobalObject(JSContext *cx, JSObject *obj)
     CHECK_REQUEST(cx);
 
     cx->globalObject = obj;
-    cx->compartment = obj ? obj->getCompartment(cx) : cx->runtime->defaultCompartment;
+    if (!cx->maybefp())
+        cx->compartment = obj ? obj->getCompartment(cx) : cx->runtime->defaultCompartment;
 }
 
 class AutoResolvingEntry {
@@ -1334,10 +1333,14 @@ JS_InitStandardClasses(JSContext *cx, JSObject *obj)
 {
     CHECK_REQUEST(cx);
 
-    if (cx->globalObject)
-        assertSameCompartment(cx, obj);
-    else
+    /*
+     * JS_SetGlobalObject might or might not change cx's compartment, so call
+     * it before assertSameCompartment. (The API contract is that *after* this,
+     * cx and obj must be in the same compartment.)
+     */
+    if (!cx->globalObject)
         JS_SetGlobalObject(cx, obj);
+    assertSameCompartment(cx, obj);
 
     /* Define a top-level property 'undefined' with the undefined value. */
     JSAtom *atom = cx->runtime->atomState.typeAtoms[JSTYPE_VOID];
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 34198f88508..35a12295877 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -957,6 +957,12 @@ JS_RewrapObject(JSContext *cx, JSObject **objp);
 extern JS_PUBLIC_API(JSBool)
 JS_RewrapValue(JSContext *cx, jsval *p);
 
+extern JS_FRIEND_API(JSCompartment *)
+js_SwitchToCompartment(JSContext *cx, JSCompartment *compartment);
+
+extern JS_FRIEND_API(JSCompartment *)
+js_SwitchToObjectCompartment(JSContext *cx, JSObject *obj);
+
 #ifdef __cplusplus
 JS_END_EXTERN_C
 
@@ -982,14 +988,20 @@ class JS_PUBLIC_API(JSAutoCrossCompartmentCall)
     }
 };
 
-class JS_FRIEND_API(JSAutoEnterCompartment)
+class JSAutoEnterCompartment
 {
     JSContext *cx;
     JSCompartment *compartment;
   public:
-    JSAutoEnterCompartment(JSContext *cx, JSCompartment *newCompartment);
-    JSAutoEnterCompartment(JSContext *cx, JSObject *target);
-    ~JSAutoEnterCompartment();
+    JSAutoEnterCompartment(JSContext *cx, JSCompartment *newCompartment) : cx(cx) {
+        compartment = js_SwitchToCompartment(cx, newCompartment);
+    }
+    JSAutoEnterCompartment(JSContext *cx, JSObject *target) : cx(cx) {
+        compartment = js_SwitchToObjectCompartment(cx, target);
+    }
+    ~JSAutoEnterCompartment() {
+        js_SwitchToCompartment(cx, compartment);
+    }
 };
 
 JS_BEGIN_EXTERN_C