popup window at chrome extensions' context menu
===

I'm developing a chrome extension and have a problem. I've added an item to chrome's context menu and want to open a popup window if the menu item is clicked. My code looks like this:

    function popup(url) {
    window.open(url, "window", "width=600,height=400,status=yes,scrollbars=yes,resizable=yes");
    }
    
    chrome.contextMenus.create({"title": "Tumblr", "contexts":["page","selection","link","editable","image","video","audio"], "onclick": popup('http://example.com')});

But this code doesn't work as I want. The popup window doesn't appear after an click on the context item, but rather after a refresh of the extension in the chrome extension preferences.

Thanks in advance!