I have use a laptop with a mouse, and I have the touch pad enabled. When I have just one PDF open the touch pad will scroll through only the PDF while the mouse wheel will still scroll through websites in other tabs. However if I open a second PDF the mouse wheel will cease to scroll through other sites and only work in that document. I have the latest version of adobe reader as the default PDF viewer. Also, if I leave a PDF document open when I leave the computer my stumbleupon toolbar will have switched places with my bookmarks toolbar when I come back; restarting Firefox always fixes this, though.