Yahoo! mail module is based on Pop3 protocol, if you are using a yahoo.com address you need to subscribe to Yahoo! Mail Plus for using it. You will find all the information you need at:

http://help.yahoo.com/help/us/mail/pop/pop-40.html

If you are not a Yahoo! Mail Plus subscriber we are really sorry because you can not use this module, but we are busily looking for solution which will work for all Users.

If you are not using yahoo.com address you need to activate the option into the Yahoo settings.

Ex:
Yahoo.fr: http://eur.help.yahoo.com/help/fr/mail/pop/pop-10.html
Yahoo.co.uk: http://eur.help.yahoo.com/help/uk/mail/pop/pop-10.html

When clicking 'Show website' inside a Feedreader, the website doesn't always remain inside the Iframe. This is because the website has scripted the site in such a way that does not permit an aggregator like netvibes to keep it within its page.

If this is an issue for you, please notify the website directly.