I can not find your original question.

Exactly what is not working ? I am using firefox including Firefox 5 on an XP and the page up and down works ok for me, eg on this forum, if I use the keyboard buttons or if I click on the scrollbar

John, I have a dell C630 with XP. I got a message about updating to FF5, prefering it to MS8 I clicked ok. Now I can not use my up down arrows or the up/down page keys. I can scroll up or down with the mouse on the skrool bar. My mouse works fine, and the page up/down works on any other program like note pad, word, excel, AVG, Norton Ghost, anything but FF5. I've checked everything I can find to check and found nothing that will cause the up/down to work in every program except FF5, and it worked fine in FF4.

If you inadvertently turned on Caret Browsing, the action of those keys would be changed to navigating with a "caret" on the page, instead of scrolling the entire page.

F7 toggles Caret Browsing on / off.
http://kb.mozillazine.org/Accessibility.browsewithcaret

Thank you