That is auto-scrolling. The speed depends on the distance that you move to mouse away from the circle. So if you scroll too fast then you have moved to the mouse to far from that circle.

Is there any way to adjust the sensitivity or the distance to make the page scroll slower? Even if I keep the mouse very close the circle it scrolls too fast for reading.I'm trying to do "hands-off" reading.

Open the computers control panel. Look for the mouse program. Look thru the settings.

There is an option to adjust how many lines the scrolling wheel skips but nothing about auto-scroll.I tested it. It seems like if I use the Auto-scroll and keep the mouse literally 1 pixel below the circle, it will be barely slow enough for reading long articles but you really have to spend a minute and a magnifier to make sure you put the mouse pointer exactly 1 pixel below the circle, otherwise it gets too fast.I'm NOT exaggerating the 1 pixel part. My screen is 1920x1080.Maybe that makes things worse. I was hoping to adjust the number of "pixels" the pointer has to travel to increase the speed from 1st to 2nd stage.Basically, to increase the distance you have to move the mouse in order to increase the acceleration. I'm not sure if anyone here uses 1080p screen.Could you please confirm that it's also 1 pixel for you ?

I've called the big guys to help you. Good luck.

Someone made a similar suggestion here but it was marked as duplicate. https://bugzilla.mozilla.org/show_bug.cgi?id=291134

I've also tried ScrollyFox addon but it didn't help.