1693061 - Selected tab is scrolled into view when a window-modal dialog shows in the browser

Status: VERIFIED FIXED

(Firefox :: Tabbed Browser, defect)

Description

[:Gijs (he/him)]

When a window-modal dialog like the multi-tab quit warning shows up, we scroll the selected tab into view. This is a bit disconcerting. The tabstrip shouldn't be impacted by the dialog showing up.

Comment 1

[:Gijs (he/him)]

This is triggered because an overflow event fires, so we hit this code. This is fairly easy to see in the browser debugger by adding a breakpoint to ensureElementIsVisible in the arrow scrollbox custom element. I don't understand why this event fires - the tabstrip isn't changing so there shouldn't be an event. Emilio, any idea what's going on there?

We could potentially avoid re-running the code there if the overflow attribute is already set on the scrollbox, but I don't know what that would break...

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: JS stack

Comment 3

[Emilio Cobos Álvarez [:emilio]]

Attachment: Native stack

So basically showing the dialog is causing the whole frame tree to blow up (nsCSSFrameConstructor::ConstructDocElementFrame), so we lose the overflow state which lives there.

Comment 4

[Emilio Cobos Álvarez [:emilio]]

Ah, there we go, changing -moz-user-input reconstructs the frames, wat: https://searchfox.org/mozilla-central/rev/5120ec68572d946bd15101cf2ee2eaf4a210724f/layout/style/nsStyleStruct.cpp#3092

Comment 5

[Emilio Cobos Álvarez [:emilio]]

Well, that line goes back to bug 78695, but we don't use mUserInput to determine stuff when we construct frames, so I think we should just remove it.

Comment 6

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1693061 - Don't make -moz-user-input differences rebuild frames. r=#layout-reviewers,#style

We don't use it for anything resembling frame construction, so this
should be safe.

This goes back to bug 78695.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a45742c9557d
Don't make -moz-user-input differences rebuild frames. r=layout-reviewers,mats

Comment 8

[Noemi Erli[:noemi_erli]]

https://hg.mozilla.org/mozilla-central/rev/a45742c9557d

Comment 9

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1685313

Comment 10

[Itiel]

Fixed on latest Nightly.