终于找到了

Excellent! Beautiful auto fade feature ,this add on is just as good as Noai Scrollbars which is a legacy add on and hasn't been updated!

The implementation seems a bit bloated with by loading the whole jQuery library just for this, and including a backup file in the extension (which is useless to users).

But it works well!

The extension is working, and it replaces the scroll bar. But after some time, the extension just stops working, and all the pages simply cannot be scrolled anymore. The plugin has to be disabled, and re-enabled again to work...