With this extension, you can customize smooth scroll behavior. The extension is worth to use, if you are frustrated at any of below. - Step size for scrolling by the cursor keys is so short. - A built-in smooth scrolling is somewhat less sensitive and laggy. - When you flick a wheel so quick, it should scrolls farther but just count ticks of a wheel. - When you flick a wheel so much on a loooong web page, it should scrolls farther. Of cource the "Access your data for all websites" permission request is for overriding scroll behavior. For instance it needs website's geometric data to know which is scrollable. You may would like to read https://support.mozilla.org/en-US/kb/permission-request-messages-firefox-extensions for more info. Source code: https://bitbucket.org/kataho/yass/src/YASS-master/YASS-WE/