In Firefox 58.02 (having also recently upgraded my Mac's OS to 10.11.6), I find the default behavior of clicking in the scrollbar has changed to "scrolling one page at a time" instead of to the point clicked. I understand that holding 'option' and clicking is a workaround, but I would prefer to be able to determine myself the default behavior (as I have in System Preferences; I am also aware of the discussion at https://support.mozilla.org/en-US/questions/1190974 but restarting does not seem to prevent this from being a persistent problem in my case).