Open to tabs.  One tab should have a refreshing page, like
http://radioparadise.com/.

The other tab should have a regular web page... maybe pick something that
is vertically long, like
http://java.sun.com/j2se/1.4/docs/guide/jni/spec/design.doc.html or
something with a text widget, like
http://bugzilla.gnome.org/enter_bug.cgi?product=galeon&version=1.2.5

Now, focus a widget in the second tab... click on the background of the
page and start pressing down to scroll with the keyboard, or click in
text-field if you have one and start typing stuff.

Now watch the first tab (with radioparadise).  When that tab refreshes (and
the tab color turns green), the current widget in the second tab loses
focus.  This is evidenced by "down" not working anymore or the text cursor
disappearing.