diff --git a/xpinstall/src/nsJSFile.cpp b/xpinstall/src/nsJSFile.cpp
index 402838978f8..b120980f485 100644
--- a/xpinstall/src/nsJSFile.cpp
+++ b/xpinstall/src/nsJSFile.cpp
@@ -71,12 +71,6 @@ extern PRBool ConvertJSValToBool(PRBool* aProp,
                                 JSContext* aContext,
                                 jsval aValue);
 
-extern PRBool ConvertJSValToObj(nsISupports** aSupports,
-                               REFNSIID aIID,
-                               const nsString& aTypeName,
-                               JSContext* aContext,
-                               jsval aValue);
-
 extern JSObject *gFileSpecProto;
 extern JSClass InstallClass;
 
diff --git a/xpinstall/src/nsJSFileSpecObj.cpp b/xpinstall/src/nsJSFileSpecObj.cpp
index a7ff6569d2a..e52b551b17c 100644
--- a/xpinstall/src/nsJSFileSpecObj.cpp
+++ b/xpinstall/src/nsJSFileSpecObj.cpp
@@ -56,12 +56,6 @@ extern PRBool ConvertJSValToBool(PRBool* aProp,
                                 JSContext* aContext,
                                 jsval aValue);
 
-extern PRBool ConvertJSValToObj(nsISupports** aSupports,
-                               REFNSIID aIID,
-                               const nsString& aTypeName,
-                               JSContext* aContext,
-                               jsval aValue);
-
 
 
 static void PR_CALLBACK
diff --git a/xpinstall/src/nsJSInstallTriggerGlobal.cpp b/xpinstall/src/nsJSInstallTriggerGlobal.cpp
index 14eaf7349ab..49ae9a8fa67 100644
--- a/xpinstall/src/nsJSInstallTriggerGlobal.cpp
+++ b/xpinstall/src/nsJSInstallTriggerGlobal.cpp
@@ -70,12 +70,6 @@ extern PRBool ConvertJSValToBool(PRBool* aProp,
                                 JSContext* aContext,
                                 jsval aValue);
 
-extern PRBool ConvertJSValToObj(nsISupports** aSupports,
-                               REFNSIID aIID,
-                               const nsString& aTypeName,
-                               JSContext* aContext,
-                               jsval aValue);
-
 PR_STATIC_CALLBACK(void)
 FinalizeInstallTriggerGlobal(JSContext *cx, JSObject *obj);
 
diff --git a/xpinstall/src/nsJSInstallVersion.cpp b/xpinstall/src/nsJSInstallVersion.cpp
index ac77526ddab..54293855d02 100644
--- a/xpinstall/src/nsJSInstallVersion.cpp
+++ b/xpinstall/src/nsJSInstallVersion.cpp
@@ -71,7 +71,7 @@ FinalizeInstallVersion(JSContext *cx, JSObject *obj);
 //
 JSClass InstallVersionClass = {
   "InstallVersion",
-  JSCLASS_HAS_PRIVATE,
+  JSCLASS_HAS_PRIVATE | JSCLASS_PRIVATE_IS_NSISUPPORTS,
   JS_PropertyStub,
   JS_PropertyStub,
   GetInstallVersionProperty,
diff --git a/xpinstall/src/nsJSWinProfile.cpp b/xpinstall/src/nsJSWinProfile.cpp
index ea01b887cf5..d2023dc6d73 100644
--- a/xpinstall/src/nsJSWinProfile.cpp
+++ b/xpinstall/src/nsJSWinProfile.cpp
@@ -56,12 +56,6 @@ extern PRBool ConvertJSValToBool(PRBool* aProp,
                                 JSContext* aContext,
                                 jsval aValue);
 
-extern PRBool ConvertJSValToObj(nsISupports** aSupports,
-                               REFNSIID aIID,
-                               const nsString& aTypeName,
-                               JSContext* aContext,
-                               jsval aValue);
-
 
 static void PR_CALLBACK
 WinProfileCleanup(JSContext *cx, JSObject *obj);
diff --git a/xpinstall/src/nsJSWinReg.cpp b/xpinstall/src/nsJSWinReg.cpp
index 5d093c83987..962e624f72d 100644
--- a/xpinstall/src/nsJSWinReg.cpp
+++ b/xpinstall/src/nsJSWinReg.cpp
@@ -58,12 +58,6 @@ extern PRBool ConvertJSValToBool(PRBool* aProp,
                                 JSContext* aContext,
                                 jsval aValue);
 
-extern PRBool ConvertJSValToObj(nsISupports** aSupports,
-                               REFNSIID aIID,
-                               const nsString& aTypeName,
-                               JSContext* aContext,
-                               jsval aValue);
-
 
 static void PR_CALLBACK WinRegCleanup(JSContext *cx, JSObject *obj)
 {