reading on-line, assist

[hfs2]

Is there a 'reader' setting/program/plugin ...
that will highlight (mildly) multiple lines of text
and do so via mouse pointer control?

I find when reading textbooks on-line it's hard to
keep my eye where it should be. If I could move
a mouse down a page as I read and have, say,
three lines highlighted text follow as it moved, it might
be easier.

I can highlight text now in ie. But it's not a scrollable
thing and it's BOLD blue. Hard on the eyes.

Even BETTER, have these three lines highlighted in the
middle of the page and use the scroll arrows.

Thanks.