I have Winds 8.1 on a Lenovo laptop.

When I scroll on file explorer it's too fast.

I have been to the "change how far you scroll with the mouse wheel"

and set it to scroll 1 line at a time,

in settigs but it hasn't slowed down.

Scorlling in Firefox is fine but does anybody know how I can make

the scrolling speed in File Explorer slower.

I'm not sure what you mean.

Press the Windows key on your keyboard

In the resulting dialogue box type:

mouse speed.

Look above where you typed and click the icon for change the mouse pointer or speed.

Now see if there's a setting you like. If not, next time type

mouse

and choose another option.

How many HID Mice do you have active your system?

On my Acer Laptop running Win7 I have a built-in Synaptic Touchpad and use a generic USB Wireless Mouse.

Each device may have it's own driver (and settings) but my Windows OS doesn't differentiate the control panel mouse settings cpl applet for the two devices.

So, even though my laptop has the Synaptic cpl applet installed, once the generic Wireless Mouse is connected and active, any changes to the cpl applet only affects how the generic Wireless Mouse functions (even though it's labeled for the Touchpad).

If I then want to make changes to how the Synaptic TouchPad functions while the generic Wireless Mouse is still connected and being used I have to select an added tab in the control panel/ mouse / cpl applet labeled "[synaptic logo] Device Settings", select the TouchPad and select "Settings..." and make separate adjustments in a pop-up window titled: "Properties for Synaptic TouchPad V7.4 on PS/2 Port".

It's just how it is (or was, since it's no longer a supported OS).