How to Change Firefox Mouse Wheel Scroll Speed?

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Xah Lee, 2011-05-30

① In the url field, type about:config.
② Scroll down to “mousewheel.withnokey.sysnumlines”. Double-click the line to set the value to “false”.
③ Double-click the line “mousewheel.withnokey.numlines”, and set it to a number you like.

The change is immediate. You don't need to restart Firefox. This works in Linux too.

In a similar way, you can get mouse wheel to scroll one-page at a time. You can also adjust the mouse wheel tilt to do page up/down instead of horizontal scroll.

Set Mouse Wheel to Page Up/Down

① Click on “mousewheel.withnokey.action” line.
② Set the value to 1.

This will make the scroll wheel to go by pages.

Tech Detail

Here's tech detail, from the official doc at Source kb.mozillazine.org.

The mousewheel variables has these 2 forms:

mousewheel.‹modifier key›.‹type›
mousewheel.horizscroll.‹modifier key›.‹type›

The ‹modifier key› key is one of: “withaltkey”, “withcontrolkey”, “withmetakey”, “withnokey”, “withshiftkey”

Type is one of: “action”, “numlines”, “sysnumlines”.

Possible Action Values

The important part is the values for the action. The action code determines whether you are scrolling by pixels, lines, pages, etc. Here are the possible values and meaning:

0 - Scroll document by a number of lines (given by the numlines property)
1 - Scroll document by one page
2 - Move back/forward in history
3 - Make text larger/smaller
4 - Scroll document by a number of pixels (given by the numlines property)

numlines

number of lines to scroll by if action is set to value 0, or pixels if action is set to value 4; otherwise, this value is ignored.

sysnumlines

use system preferences to determine how many lines to scroll by