Page up and page down keys usually don't work in the latest version of Firefox. I say 'usually' because they will start working again at (what seems to me) random times. I have NOT activated caret browsing; the arrow keys work when the page up/down keys don't. Page up/down keys work in all other apps and browsers.

In Firefox, it acts as though 'number lock' is activated - while typing this, I tried the 'end' and 'page up' keys and it typed the numbers, even though number lock is definitely not on (if I try it in another app, it doesn't type numbers but acts as page up/down etc.)