I think that's only available in FBreaderJ, if at all. Autoscrolling is
one of the *most* requested features, and so far the answer has
been...it would require a major rewrite of FBreader. FBreaderJ may be a
different story.
I believe FBreaderJ is only for Google Android phones e.g. the G1. I
don't believe it works on a laptop.
FBreaderJ is available at http://www.fbreader.org/FBReaderJ/