I do not know of a way to do that. You can only set the scroll amount for the mouse wheel via the mousewheel prefs on the about:config page, but you can't do that for the keyboard navigation keys.

That actually gave me an idea which i then used to fix the problem. thanks cor-el

For anyone that has this problem, do the following:

1. Go to about:config
2. Scroll to mousewheel.withcontrolkey.action
3. Change Value column value to 1
4. Restart Firefox

And that is how I fixed the problem

That pref determines what happens if you rotate the mouse scroll wheel while the CTRL key is pressed.
The normal action is to zoom the page.

Or could've tried SmoothWheel.

https://addons.mozilla.org/en-US/firefox/addon/smoothwheel/?src=ss

Yes, there are extension that work both for the mouse and the keyboard, but they can only be set to scroll an amount of pixels and not to scroll one line regardless of font-size (height) of the text.

• SmoothWheel: https://addons.mozilla.org/firefox/addon/smoothwheel/
• Yet Another Smooth Scrolling: https://addons.mozilla.org/firefox/addon/yet-another-smooth-scrolling/

Fixed it with following modifications to about:config:

Mouse Scroll: mousewheel.withnokey.numlines = 2

mousewheel.withnokey.sysnumlines = false

The second one is defaulted to true, which uses the OS's setting. Using a value of 1 will be a single line but feels slow. Using a value of 2 on the first setting seems more like the old scroll speed, since 6 is the new default

Keyboard:

toolkit.scrollbox.verticalScrollDistance = 2