
This feature lets you subscribe to feeds from a list of reader option that comes with the default installation, but sadly there is no entry for Pageflakes at the moment. Now, to have Pageflakes in your list of options , there is a way that I've found from Mozilla Links , which describes a way for adding your own custom feed reader to the list.
From that article, i have created the following link for you , that will do the work for you right away and let you subscribe feeds using Pageflakes from right this moment.

This will also mark Pageflakes as the default selection in the dropdown list, just check the "Always use Pageflakes to subscribe to feeds" option and that's it.

Note:You need to visit Pageflakes and setup your page first before applying the above mentioned procedure.