Link URI re: issue 486

The proposed changes address the silent failing of adding a link to an unrecognized URI. They allow the user to correct any potential mistakes made to the initial address through a prompt dialogue. 
You can make this "simpler" (i.e. defer URL parsing logic to Firefox) using nsIURL

```
if (!title) {
    var uri = Components.classes["@mozilla.org/network/io-service;1"]
        .getService(Components.interfaces.nsIIOService);
        .newURI(url, null, null);

    if (uri.scheme == 'http' || uri.scheme == 'https') {
        uri = uri.QueryInterface(Components.interfaces.nsIURL);
        if (uri.fileName) {
            title = uri.fileName;
        } else if (uri.directory) {
            var dir = uri.directory.split('/');
            title = dir[dir.length - 2];
        }

        if (!title) title = uri.scheme + '://' + uri.hostPort + uri.filePath;
    } else {
        title = url;
    }
}