To search Stumbleupon only for pages containing topics
of your special interest, you can always go to
and select one of your favourite tags or enter a
search term into the searchbox on top, to find
"stumblers" having the same interests as you,
where you can follow their links.
An advantage of this method is, that you can also
by selecting and highlighting the given URL, and
go there by the right click context menu > GoToURL.
You can avoid in this way the existing risks of all
Ajax using methods, where you will not know, what
webpages will have.
Another possibility would be to use the demo,
starting with the sites of recent popularity at