--- a/js/xpconnect/src/XPCWrappedJS.cpp
+++ b/js/xpconnect/src/XPCWrappedJS.cpp
@@ -6,17 +6,16 @@
 
 /* Class that wraps JS objects to appear as XPCOM objects. */
 
 #include "xpcprivate.h"
 #include "nsAtomicRefcnt.h"
 #include "nsProxyRelease.h"
 #include "nsThreadUtils.h"
 #include "nsTextFormatter.h"
-#include "nsCycleCollectorUtils.h"
 
 // NOTE: much of the fancy footwork is done in xpcstubs.cpp
 
 NS_IMETHODIMP
 NS_CYCLE_COLLECTION_CLASSNAME(nsXPCWrappedJS)::TraverseImpl
    (NS_CYCLE_COLLECTION_CLASSNAME(nsXPCWrappedJS) *that, void *p,
     nsCycleCollectionTraversalCallback &cb)
 {
@@ -146,34 +145,30 @@ nsXPCWrappedJS::QueryInterface(REFNSIID 
 // collection. Code in XPCJSRuntime watches for JS gc to happen and will do
 // the final release on wrappers whose JSObjects get finalized. Note that
 // even after tranistioning to this refcount-of-one state callers might do
 // an addref and cause us to re-root the JSObject and continue on more normally.
 
 nsrefcnt
 nsXPCWrappedJS::AddRef(void)
 {
-    if (!MOZ_LIKELY(NS_IsMainThread() || NS_IsCycleCollectorThread()))
-        MOZ_CRASH();
     nsrefcnt cnt = NS_AtomicIncrementRefcnt(mRefCnt);
     NS_LOG_ADDREF(this, cnt, "nsXPCWrappedJS", sizeof(*this));
 
     if (2 == cnt && IsValid()) {
         XPCJSRuntime* rt = mClass->GetRuntime();
         rt->AddWrappedJSRoot(this);
     }
 
     return cnt;
 }
 
 nsrefcnt
 nsXPCWrappedJS::Release(void)
 {
-    if (!MOZ_LIKELY(NS_IsMainThread() || NS_IsCycleCollectorThread()))
-        MOZ_CRASH();
     NS_PRECONDITION(0 != mRefCnt, "dup release");
 
     if (mMainThreadOnly && !NS_IsMainThread()) {
         // We'd like to abort here, but this can happen if someone uses a proxy
         // for the nsXPCWrappedJS.
         nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
         // If we can't get the main thread anymore we just leak, but this really
         // shouldn't happen.
@@ -277,20 +272,16 @@ CheckMainThreadOnly(nsXPCWrappedJS *aWra
 // static
 nsresult
 nsXPCWrappedJS::GetNewOrUsed(JSContext* cx,
                              JSObject* aJSObj,
                              REFNSIID aIID,
                              nsISupports* aOuter,
                              nsXPCWrappedJS** wrapperResult)
 {
-    // Do a release-mode assert against accessing nsXPCWrappedJS off-main-thread.
-    if (!MOZ_LIKELY(NS_IsMainThread() || NS_IsCycleCollectorThread()))
-        MOZ_CRASH();
-
     JS::RootedObject jsObj(cx, aJSObj);
     JSObject2WrappedJSMap* map;
     nsXPCWrappedJS* root = nullptr;
     nsXPCWrappedJS* wrapper = nullptr;
     nsXPCWrappedJSClass* clazz = nullptr;
     XPCJSRuntime* rt = nsXPConnect::GetRuntimeInstance();
     JSBool release_root = false;
 
@@ -563,20 +554,16 @@ nsXPCWrappedJS::GetInterfaceInfo(nsIInte
     return NS_OK;
 }
 
 NS_IMETHODIMP
 nsXPCWrappedJS::CallMethod(uint16_t methodIndex,
                            const XPTMethodDescriptor* info,
                            nsXPTCMiniVariant* params)
 {
-    // Do a release-mode assert against accessing nsXPCWrappedJS off-main-thread.
-    if (!MOZ_LIKELY(NS_IsMainThread() || NS_IsCycleCollectorThread()))
-        MOZ_CRASH();
-
     if (!IsValid())
         return NS_ERROR_UNEXPECTED;
     if (NS_IsMainThread() != mMainThread) {
         NS_NAMED_LITERAL_STRING(kFmt, "Attempt to use JS function on a different thread calling %s.%s. JS objects may not be shared across threads.");
         PRUnichar* msg =
             nsTextFormatter::smprintf(kFmt.get(),
                                       GetClass()->GetInterfaceName(),
                                       info->name);

new file mode 100644
--- /dev/null
+++ b/js/xpconnect/tests/unit/test_bug608142.js
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: sw=4 ts=4 sts=4 et
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function run_test() { 
+    var tm = Components.classes["@mozilla.org/thread-manager;1"].getService();
+    var thr = tm.newThread(0);
+
+    var foundThreadError = false;
+ 
+    var listener = {
+        observe: function(message) {
+            if (/JS function on a different thread/.test(message.message))
+                foundThreadError = true;
+        }
+    };
+
+    var cs = Components.classes["@mozilla.org/consoleservice;1"].
+        getService(Components.interfaces.nsIConsoleService);
+    cs.registerListener(listener);
+
+    thr.dispatch({
+        run: function() {
+            do_check_true(false);
+        }
+    }, Components.interfaces.nsIThread.DISPATCH_NORMAL);
+
+    thr.shutdown();
+
+    cs.unregisterListener(listener);
+    do_check_true(foundThreadError);
+}
+

--- a/js/xpconnect/tests/unit/xpcshell.ini
+++ b/js/xpconnect/tests/unit/xpcshell.ini
@@ -2,16 +2,17 @@
 head = 
 tail = 
 
 [test_bogus_files.js]
 [test_bug408412.js]
 [test_bug451678.js]
 [test_bug596580.js]
 [test_bug604362.js]
+[test_bug608142.js]
 [test_bug641378.js]
 [test_bug677864.js]
 [test_bug711404.js]
 [test_bug778409.js]
 [test_bug780370.js]
 [test_bug805807.js]
 [test_bug809652.js]
 [test_bug813901.js]