1797964 - position fixed at bottom moves around on scroll

Status: NEW

(Fenix :: 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

[miralobontiu]

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

[miralobontiu]

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

[miralobontiu]

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