Error when opening the extensions manager from Xul app

Question

When I open the extensions manager in my Xul app using:

app = "chrome://mozapps/content/extensions/extensions.xul";
window.open(app,'Test','chrome, width=640, height=480').moveTo(0,0);

I get the following error in the javascript console:

Error: uncaught exception: [Exception... "Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED) [nsIPrefBranch2.getBoolPref]" nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)" location: "JS frame :: chrome://mozapps/content/extensions/extensions.js :: updateGlobalCommands :: line 2388" data: no]

Any idea what's this?

ps. The extensions manager opens and works well, but I'm worried with this error message.