I'm having trouble using the up & down arrow keys to scroll in firefox on my keyboard on a macbook air. It stops working when I click somewhere on the page.
When I open an internet page and start scrolling using my up and down arrow keys on the keyboard the page goes up and down just fine. The problem comes when I click somewhere on the page and suddenly using the up and down arrows on the keyboard is like scrolling up and down the text, like in a word document. The cursor is suddenly scrolling through the text on the internet page instead of scrolling up and down the page as a whole. Or it just goes straight to the bottom of the page and then I am not able to use the arrow keys to go anywhere else on the page.
You may have inadvertently turned on caret browsing. There would be a flashing cursor appearing where you clicked on the page, and the arrow keys will navigate 'up' or 'down' thru the text on the page and not scroll the entire page.
Hit F7 to turn it off and then see if your issue is corrected.