After you install - If you don't see any change on a page that was loaded before you installed this style then Reload the page.

test it here -
http://trac.webkit.org/export/41842/trunk/LayoutTests/scrollbars/overflow-scrollbar-combinations.html

See also my http://freestyler.ws/style/125430/scrollbars-to-menus-adjustable-height

And also my http://freestyler.ws/style/105332/black-menus-and-tooltips

Note : The style excludes some sites in which a wide scrollbar somerimes hides text.
[Tell me if you find some other sites that you think they should also be excluded] :
mail.yahoo
mail.google.
drive.google
evernote
pinterest
facebook
twitter
soundcloud


Based on Antonio Ferreiro "a3cAnton"'s http://freestyler.ws/style/105208/firefox-nightblue-scrollbars-by-a3canton