diff --git a/js/src/xpconnect/src/XPCSafeJSObjectWrapper.cpp b/js/src/xpconnect/src/XPCSafeJSObjectWrapper.cpp
index e5b3ae525846..130d106c8fe5 100644
--- a/js/src/xpconnect/src/XPCSafeJSObjectWrapper.cpp
+++ b/js/src/xpconnect/src/XPCSafeJSObjectWrapper.cpp
@@ -867,7 +867,8 @@ XPC_SJOW_Construct(JSContext *cx, JSObject *obj, uintN argc, jsval *argv,
   obj = nsnull;
 
   if (JSVAL_IS_PRIMITIVE(argv[0])) {
-    return ThrowException(NS_ERROR_INVALID_ARG, cx);
+    *rval = argv[0];
+    return JS_TRUE;
   }
 
   JSObject *objToWrap = JSVAL_TO_OBJECT(argv[0]);
diff --git a/netwerk/base/src/nsProxyAutoConfig.js b/netwerk/base/src/nsProxyAutoConfig.js
index 492c4bd711a3..5e40925c1913 100644
--- a/netwerk/base/src/nsProxyAutoConfig.js
+++ b/netwerk/base/src/nsProxyAutoConfig.js
@@ -96,16 +96,17 @@ nsProxyAutoConfig.prototype = {
             return null;
 
         // Call the original function
-        var rval = this._sandBox.FindProxyForURL(testURI, testHost);
+        try {
+            var rval = this._sandBox.FindProxyForURL(testURI, testHost);
+        } catch (e) {
+            throw new XPCSafeJSObjectWrapper(e);
+        }
         return rval;
     }
 }
 
 function proxyAlert(msg) {
-    // Ensure that we have a string.
-    if (typeof msg != "string")
-        msg = new XPCSafeJSObjectWrapper(msg).toString();
-
+    msg = new XPCSafeJSObjectWrapper(msg);
     try {
         // It would appear that the console service is threadsafe.
         var cns = Components.classes["@mozilla.org/consoleservice;1"]
@@ -127,9 +128,7 @@ function myIpAddress() {
 
 // wrapper for resolving hostnames called by PAC file
 function dnsResolve(host) {
-    if (typeof host != "string")
-        host = new XPCSafeJSObjectWrapper(host).toString();
-
+    host = new XPCSafeJSObjectWrapper(host);
     try {
         return dns.resolve(host, 0).getNextAddrAsString();
     } catch (e) {