OP, there are two parts to this.
One is handles by your Desktop Environment for desktop scrolling outside of apps. Others have mentioned this.
The other is handled directly by browsers.
To enable this for browsers:
Firefox:
under about:config
, the key general.autoScroll
needs to be set to true
Chrome:
Chrome (and any electron based apps) needs to have the following additional flag added to launch with support for middle click scroll:
--enable-blink-features=MiddleClickAutoscroll
I would also advise you to map 2 of your mouse buttons to scroll up and scroll down, that way you can just hold a key down to scroll instead of shaking your mouse around using the autoscroll arrows.
Imagine being this guy above me and thinking that the percent of people that would switch out from their default shipped DE terminal emulator is anything but a minority π€ͺ