1797964 - position fixed at bottom moves around on scroll, when the address bar is at the top

Status: NEW

(Firefox for Android :: General, defect)

Description

[Pierre Ossman]

Steps to reproduce:

Position an element as:

element {
position: fixed;
bottom: 0;
}

And then scroll up and down.

Actual results:

The element jumps around a bit whenever the address bar is hidden or shown, temporarily also showing what's behind the element.

Expected results:

The element should have stayed perfectly still at the bottom.

Comment 1

[Pierre Ossman]

I'm speculating that this is caused by a delay in calculating the dimensions of the dynamic viewport. I can see the same effect by doing something like:

element {
position: fixed;
top: 95dvh;
}

This was seen with Firefox 106.1.0.

Comment 2

[Mira Lobontiu (Android QA)]

Thank you for the report!

Could ypu please retest this, and provide us some more details:

• the device you've tested with,
• the Firefox for Android version,
• a short video, if it is possible?

Comment 3

[Pierre Ossman]

Tested on a Samsung Galaxy Tab S7 with Firefox 116.3.0. Tested with a min-height: 100dvh; test case, as the original test site has been changed since the report was made.

Comment 4

[jackyzy823]

I used to encounter the similar phenomenon , but i tested today, looks like it has been fixed.

Comment 5

[Pierre Ossman]

In something newer than 116?

I tried to upload a video of the bug, but bugzilla keeps crashing when I try to attach the file. :/

Comment 6

[jackyzy823]

Sorry, I'm not fully tested, it still exists. :(

Comment 7

[Mira Lobontiu (Android QA)]

Hello again!
Could you retest this on the latest Firefox for Android 122.1.0 build with your device?
It could also help to provide us a link/page you've encountered this issue on, and a very short (< 10MB) video with the issue.
Thank you!

Comment 8

[mikaka27]

Hi, I'm not the author of this issue, but I filed a similar issue, when I was not aware of this one.
https://bugzilla.mozilla.org/show_bug.cgi?id=1876802

Could you check if maybe it's the same problem?
I have attached a website link and video there.

Comment 9

[Pierre Ossman]

(In reply to miralobontiu from comment #7)

Hello again!
Could you retest this on the latest Firefox for Android 122.1.0 build with your device?
It could also help to provide us a link/page you've encountered this issue on, and a very short (< 10MB) video with the issue.
Thank you!

I'm afraid I'm still seeing it with Firefox 122.1.0 on Samsung Galaxy Tab S7. I'll attach a test case, and hopefully also a video.

(In reply to mikaka27 from comment #8)

Hi, I'm not the author of this issue, but I filed a similar issue, when I was not aware of this one.
https://bugzilla.mozilla.org/show_bug.cgi?id=1876802

Could you check if maybe it's the same problem?
I have attached a website link and video there.

From what I can tell, it behaves just the same. So it's likely the same bug.

Comment 10

[Pierre Ossman]

Attachment: test case

Comment 11

[Pierre Ossman]

Attachment: Demonstration video

Comment 12

[mikaka27]

(In reply to Pierre Ossman from comment #9)

(In reply to miralobontiu from comment #7)

Hello again!
Could you retest this on the latest Firefox for Android 122.1.0 build with your device?
It could also help to provide us a link/page you've encountered this issue on, and a very short (< 10MB) video with the issue.
Thank you!

I'm afraid I'm still seeing it with Firefox 122.1.0 on Samsung Galaxy Tab S7. I'll attach a test case, and hopefully also a video.

(In reply to mikaka27 from comment #8)

Hi, I'm not the author of this issue, but I filed a similar issue, when I was not aware of this one.
https://bugzilla.mozilla.org/show_bug.cgi?id=1876802

Could you check if maybe it's the same problem?
I have attached a website link and video there.

From what I can tell, it behaves just the same. So it's likely the same bug.

I also can reproduce the problem on your test case (when I zoom in a little).

Comment 14

[Mira Lobontiu (Android QA)]

I was able to reproduce this issue on the wykop.pl website, and on the test case provided by the reporter on the latest Firefox for Android 123.0, with a Xiaomi mi8 Lite (Android 9) device.
Not reproduced it on today's nightly 124.0a1 from 2/13 though.
I'll confirm this issue.

Comment 15

[mikaka27]

I've noticed something, it seems to be somewhat related to font size in firefox settings.
If I have font size set at 100% the issue occurs rarely (but not never).
For example on wykop.pl I never see it on main site, but I see it when I enter my profile settings.
In this profile settings it seems I can zoom out on website further than before.

If I have font size set above 100% the issue occurs always.

Comment 16

[mikaka27]

I'm attaching the video which displays the issue with font size. Notice that each step that increases the font more above 100% breaks position: fixed element even more:
https://www.dropbox.com/scl/fi/r6n5d824ors5byi9umih3/Screen_Recording_20240526_181101_Firefox.mp4?rlkey=5amkrvmenrd8a45sz0ew7qchk&st=875eymlq&dl=0

Comment 17

[Markus Stange [:mstange]]

To reproduce this, make sure the address bar is set to display at the top.

The incorrect offset when zoomed in is tracked in bug 1880375.

Comment 19

[mail]

I am also having this issue on Samsung Galaxy S23 // Android 16 // One UI 8.0 // Firefox Android 147.0.3.
Considering the severity and the fact that this issue was opened three years ago can you please let us know when or if this will ever be fixed?

Comment 20

[Botond Ballo [:botond]]

(In reply to mail from comment #19)

can you please let us know when or if this will ever be fixed?

This bug has been identified as depending on bug 1921331, which is a project we're planning to spend time on this year.