I upgraded from Firefox 3.6 to Firefox 19 (!!! how do they manage to release sixteen major versions in just three years?), and now find that the arrow keys scroll the page by much more than they used to. Previously a single downarrow press would scroll down by about 1 line of text; now it scrolls 2 or 3 lines. That is rather annoying.
I suppose there must be some setting in about:config I can adjust to get the single-line scrolling back, but where? Searching for "scroll" in the list doesn't turn up anything promising (which works).
(I've seen various places on the web recommend the "Yet another smooth scrolling" extension, but it doesn't do quite the right thing -- it lets me control the amount of scroll alright, but even if I turn its smoothness controls all the way down to 0, it stills seems to scroll each line in two quick steps rather than immediately).