diff --git a/js/jsd/jsd_xpc.cpp b/js/jsd/jsd_xpc.cpp
--- a/js/jsd/jsd_xpc.cpp
+++ b/js/jsd/jsd_xpc.cpp
@@ -1133,32 +1133,36 @@ jsdScript::GetVersion (PRInt32 *_rval)
     ASSERT_VALID_EPHEMERAL;
     JSContext *cx = JSD_GetDefaultJSContext (mCx);
     JSScript *script = JSD_GetJSScript(mCx, mScript);
     *_rval = static_cast<PRInt32>(JS_GetScriptVersion(cx, script));
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::GetTag(PRUint32 *_rval)
 {
+    JSD_LockScriptSubsystem(mCx);
     if (!mTag)
         mTag = ++jsdScript::LastTag;
     
     *_rval = mTag;
+    JSD_UnlockScriptSubsystem(mCx);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::Invalidate()
 {
+    JSD_LockScriptSubsystem(mCx);
     ASSERT_VALID_EPHEMERAL;
     mValid = PR_FALSE;
+    JSD_UnlockScriptSubsystem(mCx);
     
     /* release the addref we do in FromPtr */
     jsdIScript *script = static_cast<jsdIScript *>
                                     (JSD_GetScriptPrivate(mScript));
     NS_ASSERTION (script == this, "That's not my script!");
     NS_RELEASE(script);
     JSD_SetScriptPrivate(mScript, NULL);
     return NS_OK;
 }
 
@@ -1178,82 +1182,94 @@ jsdScript::InvalidateAll ()
             static_cast<jsdIScript *>(JSD_GetScriptPrivate(script));
         if (jsdis)
             jsdis->Invalidate();
     }
     JSD_UnlockScriptSubsystem(cx);
 }
 
 NS_IMETHODIMP
 jsdScript::GetIsValid(PRBool *_rval)
 {
+    JSD_LockScriptSubsystem(mCx);
     *_rval = mValid;
+    JSD_UnlockScriptSubsystem(mCx);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::SetFlags(PRUint32 flags)
 {
+    JSD_LockScriptSubsystem(mCx);
     ASSERT_VALID_EPHEMERAL;
     JSD_SetScriptFlags(mCx, mScript, flags);
+    JSD_UnlockScriptSubsystem(mCx);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::GetFlags(PRUint32 *_rval)
 {
+    JSD_LockScriptSubsystem(mCx);
     ASSERT_VALID_EPHEMERAL;
     *_rval = JSD_GetScriptFlags(mCx, mScript);
+    JSD_UnlockScriptSubsystem(mCx);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::GetFileName(nsACString &_rval)
 {
     _rval.Assign(*mFileName);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::GetFunctionName(nsACString &_rval)
 {
     _rval.Assign(*mFunctionName);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::GetParameterNames(PRUint32* count, PRUnichar*** paramNames)
 {
+    JSD_LockScriptSubsystem(mCx);
     ASSERT_VALID_EPHEMERAL;
     JSContext *cx = JSD_GetDefaultJSContext (mCx);
     if (!cx) {
         NS_WARNING("No default context !?");
+        JSD_UnlockScriptSubsystem(mCx);
         return NS_ERROR_FAILURE;
     }
     JSFunction *fun = JSD_GetJSFunction (mCx, mScript);
 
     JSAutoRequest ar(cx);
 
     if (!fun || !fun->hasLocalNames() || fun->nargs == 0) {
         *count = 0;
         *paramNames = nsnull;
+        JSD_UnlockScriptSubsystem(mCx);
         return NS_OK;
     }
 
     PRUnichar **ret =
         static_cast<PRUnichar**>(NS_Alloc(fun->nargs * sizeof(PRUnichar*)));
-    if (!ret)
+    if (!ret) {
+        JSD_UnlockScriptSubsystem(mCx);
         return NS_ERROR_OUT_OF_MEMORY;
+    }
 
     void *mark = JS_ARENA_MARK(&cx->tempPool);
     jsuword *names = js_GetLocalNameArray(cx, fun, &cx->tempPool);
     if (!names) {
         NS_Free(ret);
+        JSD_UnlockScriptSubsystem(mCx);
         return NS_ERROR_OUT_OF_MEMORY;
     }
 
     nsresult rv = NS_OK;
     for (uintN i = 0; i < fun->nargs; ++i) {
         JSAtom *atom = JS_LOCAL_NAME_TO_ATOM(names[i]);
         if (!atom) {
             ret[i] = 0;
         } else {
             jsval atomVal = ATOM_KEY(atom);
@@ -1270,20 +1286,21 @@ jsdScript::GetParameterNames(PRUint32* c
                 rv = NS_ERROR_OUT_OF_MEMORY;
                 break;
             }
         }
     }
     JS_ARENA_RELEASE(&cx->tempPool, mark);
     if (NS_FAILED(rv))
         return rv;
     *count = fun->nargs;
     *paramNames = ret;
+    JSD_UnlockScriptSubsystem(mCx);
     return NS_OK;
 }
 
 NS_IMETHODIMP
 jsdScript::GetFunctionObject(jsdIValue **_rval)
 {
     JSFunction *fun = JSD_GetJSFunction(mCx, mScript);
     if (!fun)
         return NS_ERROR_NOT_AVAILABLE;