1347382 - Scrolling in tabs strip doesn't always work if mouse is placed above selected tab

Status: NEW

(Firefox :: Tabbed Browser, defect)

Description

[684sigma]

I have a problem with Firefox Beta 53. It doesn't happen in Firefox ESR 45
Sometimes scrolling in tabs strip doesn't work.
I noticed one specific scenario when it happens

1. Open many tabs so that some tabs are invisible, scroll tabs strip to the end
2. Select the leftmost (partially) visible tab. Scroll tabs strip to the end
3. Remember the place where close button of selected tab was located. Move mouse pointer to that place
4. Rotate mouse wheel down

Result: Tabs strip jumps a bit to the right, then a bit to the left. Doesn't scroll to the end
Expected: Tabs strip should scroll to the end

Comment 1

[Alice0775 White]

[Tracking Requested - why for this release]: UX regression, tabbar does not scroll properly with mouse wheel


Regression window:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=c619c89829a77ae64b0d205a8c03f49283db921c&tochange=02c94a326f6dae12438b9c1b827b88db79bf78a0

Regressed by: 	02c94a326f6d	Premang — Bug 498976 - Scroll the selected tab into view on mouseover when it's only partially visible. r=dao

Comment 2

[Alice0775 White]

screen cast : https://www.youtube.com/watch?v=botWNzFbhCg

Comment 3

[684sigma]

(In reply to Alice0775 White from comment #2)
> screen cast : https://www.youtube.com/watch?v=botWNzFbhCg

This is what Comment 0 describes, but this bug happens in more cases. I only described one case, because it was the easiest to explain.
In fact, if I hover selected tab during scrolling in tab bar, the scrolling just stops.

So, in general, "hovering any element in selected tab stops scrolling and scrolls the tab into view".
My expectation is that if scrolling is going on in tab bar, hovering selected tab should do nothing.

Comment 4

[Liz Henry (:lizzard) (relman/hg->git project)]

Too late for a fix for 53, as we are heading into the last week of the beta 53 cycle and no one is assigned.

Comment 5

[Gerry Chang [:gchang]]

Per comment #4, track 54-.

Comment 6

[Liz Henry (:lizzard) (relman/hg->git project)]

Dão, what do you think about this regression (since you are the triage owner and reviewed the patch in bug 498976). Worth fixing in 55? Or general backlog (maybe a good first bug)?

Comment 7

[Dão Gottwald [:dao]]

Not sure how we'd address this. Backing out bug 498976 might be the most sensible solution for the time being. Premang, what do you think?