1954212 - Add preferences to customize the speed of autoscroll

Status: RESOLVED FIXED

(Core :: Panning and Zooming, enhancement, P3)

Description

[Botond Ballo [:botond]]

Currently, the constants governing the speed of autoscroll animations are hard-coded.

We have received feedback from some users (Connect thread) who find the current speed too fast and would like to be able to customize it.

This bug tracks exposing the relevant constants in about:config to allow users to customize them.

Note that the autoscroll logic is found in two places in the code:

• the compositor codepath, for cases where we're able to run the animation on the compositor thread
• the main-thread codepath, for cases where we cannot

The two should remain in sync, e.g. both should respect any new preferences.

Comment 1

[Kometes]

Attachment: Bug 1954212 - Add general.autoscroll.speed_multiplier pref to scale autoscroll speed. r?botond

The autoscroll speed divisor was hardcoded (12) in two synchronized
codepaths: the compositor (gfx/layers/apz/src/AutoscrollAnimation.cpp)
and the main thread (toolkit/actors/AutoScrollChild.sys.mjs). Expose it
as a percentage multiplier pref (apz.autoscroll.speed_multiplier;
100 = default, 200 = double speed, 50 = half speed), read by both paths
and defaulting to 100 so existing behavior is unchanged. The multiplier
and resulting speed are clamped to >= 1 to avoid a zero divisor.

Comment 2

[BugBot [:suhaib / :marco]]

The following patch is waiting for review from an inactive reviewer:

ID	Title	Author	Reviewer Status
D306915	Bug 1954212 - Add general.autoscroll.speed_multiplier pref to scale autoscroll speed. r?botond	someanon10	botond: Back Jun 24, 2026

:someanon10, could you please find another reviewer?

For more information, please visit BugBot documentation.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/070102881b70
https://hg.mozilla.org/integration/autoland/rev/90d0cb734aa6
Add general.autoscroll.speed_multiplier pref to scale autoscroll speed. r=botond

Comment 4

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/90d0cb734aa6