1687828 - A scrollbar is briefly shown when transitioning a panelview between subviews

Status: RESOLVED FIXED

(Firefox :: Menus, defect)

Description

[Mike Conley (:mconley) (:⚙️)]

The easiest way to see this right now probably is to:

1. Enable Proton (browser.proton.enabled set to true)
2. Open a new window
3. Open the AppMenu/Hamburger menu, and click on "Library"
4. Note during the transition a brief appearance of a vertical scrollbar on the panel

This isn't Proton-specific - it looks this can happen when transitioning between a short subview to a tall subview.

Comment 1

[Mike Conley (:mconley) (:⚙️)]

Thankfully, PanelMultiView.jsm (the thing that powers <panelmultiview> elements) adds a transitioning="true" attribute on the panelview as it's transitioning, which we can maybe use to add overflow-y: hidden; on the subview when that attribute is present.

Note that PanelMultiView.jsm also has this cleanup function which might be relevant: https://searchfox.org/mozilla-central/rev/2c06b16a0c15ae340a0532e319cbf89ef9d21b68/browser/components/customizableui/PanelMultiView.jsm#1109-1148

It looks like there's effort to disable scrollbars entirely for things with panel-viewcontainer class.

My tentative suggestion is to add something like this:

panelmultiview[transitioning] > .panel-viewcontainer > .panel-viewstack > panelview > .panel-subview-body {
  overflow-y: hidden;
}

somewhere within https://searchfox.org/mozilla-central/rev/2c06b16a0c15ae340a0532e319cbf89ef9d21b68/browser/themes/shared/customizableui/panelUI.inc.css

In... theory that might work? But I haven't tried it.

Comment 2

[Mike Conley (:mconley) (:⚙️)]

Do you have a few moments to see if that CSS would work?

Comment 3

[Molly Howell (she/her) (mostly inactive)]

That does appear to work; the scrollbar is gone and I don't see any other artifacts. Patch forthcoming.

Comment 4

[Molly Howell (she/her) (mostly inactive)]

Attachment: Bug 1687828 - Prevent a temporary scrollbar while transitioning between subviews of a panelmultiview. r=mconley

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/01d0075921df
Prevent a temporary scrollbar while transitioning between subviews of a panelmultiview. r=mconley

Comment 6

[Alexandru Michis [:malexandru]]

https://hg.mozilla.org/mozilla-central/rev/01d0075921df