1479759 - Autoscroll starts scrolling right as soon as I middle-click

Status: NEW

(Core :: Widget, defect, P2)

Description

[Luke Usherwood]

STEPS:

  1. Have firefox on my right-hand monitor (optional, see below)
  2. Open a page that can scroll both horizontally & vertically
     (and/or resize the window until both scrollbars appear)
  3. Simply middle-click

OBSERVED: 

  The page starts immediately scrolling to the right, fairly quickly.

  In fact, the further to the right I click in *absolute* screen coordinates (hence step 1) the faster the initial scrolling is.

  The issue can be seen with FF on the left monitor, but only if I click in the right 20% or so of the window. This scrolls slowly.

EXPECTED: 

  The page should not scroll until I move my mouse away from the centre of the 4-arrow image thingy.

ADDITIONAL INFO:

 * I have two monitors at 2560x1440 resolution. Left monitor is the primary.
 * I have a custom scale factor of 115% set in Windows Settings

It seems like a miscalculation of the cursor position away from the DOT. (Intuitively, I might guess the screen scale factor is somehow not applied correctly?)

There is also a bias in the vertical direction when I click within the lower area of the screen (seen by how far away from the 'dot' I need to move the mouse) but the bias is not sufficient to start it scrolling immediately.

Comment 1

[Timea Zsoldos [:zstimi/tzsoldos], Desktop QA]

The issue cannot be reproduced on the version that is supposed to be affected, nor on Firefox 85.0.

Comment 2

[Luke Usherwood]

I've just reproduced it on my laptop with 4k resolution (single-screen). Although the following is not a realistic "real-world" configuration, it demonstrates that it still occurs, and thus can affect other real-world configurations (like my multi-monitor setup at work).

1. Windows Settings > Display Settings > Advanced. Select a CUSTOM 115% scaling factor.
2. Sign out and log back in. (Everything is so tiny I can barely read anything)
3. Zoom this very bugzilla page in fully (like to 300%, using Ctrl-+). Shrink the window if necessary to make the horizontal scroll-bar visible
4. Middle-click on the right-hand side of the firefox window. (On my laptop: a 3-finger tap on my touchpad)

The pan-to-scroll icon appears and the window starts scrolling to the right, despite me not moving the mouse cursor after tapping