[Bug] Flickery white line at bottom of page - Firefox Nightly Android

[st3fan]

Taken from https://bugzilla.mozilla.org/show_bug.cgi?id=1634969

(Images in Bugzilla bug)

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:76.0) Gecko/20100101 Firefox/76.0

Steps to reproduce:

Open a website with a dark background colour in Firefox Nightly for Android - using Oneplus 7 Pro. OxygenOS 10.0.5 based on Android 10. Nightly version 200502 06:01

Actual results:

As I scroll down I see a flickering white line at the bottom of the screen, maybe 1 or 2 pixels high.

Expected results:

No line

┆Issue is synchronized with this Jira Story

[ekager]

This sounds like a toolbar margin issue maybe?

[ekager]

Seeing a tiny 1 pixel line at the top of the screen with bottom toolbar on today's nightly.

[liuche]

Need to be in dark theme to notice.

(have top toolbar)
Force-quit app
load github, scroll around a little

sometimes it comes and goes.

[liuche]

E2 timebox

[tajnymag]

I've recorded a screencast showing the bug in motion.

[kglazko]

I've been able to reproduce this issue (I think- or else something similar looking) on Reddit. The difference is that when you scroll the webpage, you can actually see contents of the web page such as logos or text show up within the white bar. I'm attaching a screenshot and will continue to investigate tomorrow, but now I'm wondering if this is a web content issue of some kind..

[liuche]

We've added some custom behaviors on top and bottom dynamic toolbars, so this might be a side effect, and something that we're telling GV. This might be something that happens because we're telling GV the wrong value in setVerticalClipping.

Affects Reddit, etc

@Mugurell do you have any ideas about something that might be causing this "off by 1 pixel" problem?

[Mugurell]

This seems pretty bothersome though at first glance nothing stands out in code..

Trying to find a regression range got me so far that I had to use builds for FirefoxCI because locally there were issues with building off of old revisions.

I'm seeing the issue reproducing even on the oldest build available on CI (Nov 2019), even before the dynamic toolbars - https://drive.google.com/file/d/1X0zA4vVcKlFZtJ62qdf06S_-KmM2lwLn

Will investigate a bit more.

[Mugurell]

I think the white space is actually rendered by GV.
Filed https://bugzilla.mozilla.org/show_bug.cgi?id=1648079 for this.

[kglazko]

Thank you! I suspected that too :) I will make sure it is on their radar.

[Mugurell]

One very good observation from #17331 (comment)

the issue still reproduces but only when I enable dynamic address bar. If I have address bar that does not hide when I scroll down the issue doesn't exist.

[joheiska]

Having this same issue. Using static toolbar like mentioned, or zooming in even a tiny bit, seems to remove it.

85.1.3 (Build #2015792283)
AC: 70.0.20, d282b98ef
GV: 85.0.2-20210208133944
AS: 67.2.0

[karlcow]

Another instance #10598

[Dodgexander]

I have a similar issue, but only with stable, not with nightly. The issue is particularly bad when you scroll whilst using a video.. With video the whole screen flickers, when it happens without video playing there's just horizontal lines. The issue is also present when I use my on screen keyboard.

With keyboard not used, fixed address bar stable is fine.
With hidden address bar it happens when scrolling on stable.
With keyboard up it happens with scrolling and when typing on stable.
It seems to be triggered by any on screen movement, even happens with the cursor blinking waiting for text input or a moving advertisement on stable.

In nightly none of this happens at all.

Here's both about:support from stable where it's broken and nightly where it works fine.

Also attached is a screenshot showing the flickering lines on this very page.

[Mikaka27]

I still see it on nightly
91.0a1 (Build #2015819401)

Edit: Sorry I meant original issue, not yours @Dodgexander

[Mugurell]

@Dodgexander I've created https://bugzilla.mozilla.org/show_bug.cgi?id=1719280 for the issue you are seeing.
Please follow the discussion there.
If you could also post there a video of the issue it would probably help a lot.

[Nickoriginal]

Hello! Not reproducible in Firefox 90.1.1 on:
Samsung Galaxy A20s (Android 10)
@Mugurell, your bug 1719280 and main bug 1696905 both were resolved and closed (second - fixed). We should close this GitHub issue too?

[tajnymag]

@Nickoriginal, I don't think it can be closed. It's still reproducible on Firefoxu Nigthly 91.0a1 (Build #2015821707) on OnePlus 7T/Android 11.

[Nickoriginal]

Yes, impossible to reproduce in GitHub (where I tested this), but on other sites it still exists. Confirmed in Firefox 90.1.1, 90.0.0-beta.6 and Nightly 91.0a1 2021-07-12T17:08:00.346

[joheiska]

Still there and shouldnt be closed, nightly 91.0a1 on Xiaomi Mi 9T pro.

[tajnymag]

@Nickoriginal

I can even reproduce it on Github

[Mikaka27]

I can reproduce on github too, if you have dark mode enabled you won't see white line, instead if you look very closely you can see that as you scroll up/down, the fixed top header of github page is moving slightly up and down.

[Mugurell]

Hello! Not reproducible in Firefox 90.1.1 on: Samsung Galaxy A20s (Android 10)
@Mugurell, your [bug 1719280](https://bugzilla.mozilla.org/show_bug.cgi?id=1719280) and main [bug 1696905](https://bugzilla.mozilla.org/show_bug.cgi?id=1696905) both were resolved and closed (second - fixed). We should close this GitHub issue too?

That was a different issue than the one from this ticket.

For this issue there are other Bugzilla tickets open, like
https://bugzilla.mozilla.org/show_bug.cgi?id=1654632
https://bugzilla.mozilla.org/show_bug.cgi?id=1648079
The issue quite tricky to identify and solve.

[Mugurell]

Removing this from our sprint since we depend on GeckoView for a fix.

[Nickoriginal]

@tajnymag @Mikaka27 Thanks, I didn't saw it before, it is very small.

[plwt]

User feedback - https://support.mozilla.org/en-US/questions/1350017

[tajnymag]

Any updates? The issue is still present in the latest Nightly.

[stale]

See: #17373 This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Mugurell]

I think this was resolved by https://bugzilla.mozilla.org/show_bug.cgi?id=1734261 and the fix should be available in nightly and beta.
Closing the ticket as fixed instead of wontfix.
If the problems persists this can be reopened for more investigation.