1222335 - Some Steam Community Profile icons don't show due to <img srcset> loaded in iframe

Status: RESOLVED DUPLICATE of bug 1166138

(Core :: Layout: Images, Video, and HTML Frames, defect)

Description

[s.rittby]

Attachment: image displaying the 'missing images' and the one present image. Friend's username censored for privacy reasons.

User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0
Build ID: 20151029151421

Steps to reproduce:

Went to my Steam profile page (https://steamcommunity.com/id/mardanthedestroyer) and clicked on the middle image in the screenshot showcase's sidebar.


Actual results:

In the popup, the Profile images related to comments (the profile images in front of comments and on the comment submission form) displayed the *broken image* placeholder.


Expected results:

The images should have displayed normally.

Comment 1

[Loic]

Attachment: iframe.html

Comment 2

[Loic]

Attachment: testcase.html

Regression range:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=09f4968d5f42&tochange=9696d1c4b3ba

Workaround: dom.image.srcset.enabled=false helps (bug 1018389 where image srcset is on by default)

I think it's related to a preloading issue of <img srcset> in iframe.
It's reproducible with a simple testcase where images are in iframe loaded with fading. When you hovers the red <div> for the 1st time, the purple iframe is loaded with images faded in but not displayed.

Comment 3

[Loic]

Attachment: 1222335.zip (reduced testcase of Steam website)

I add a reduced testcase of the Steam Community website. There is still a lot of JS but the issue is more visible by just opening the file "Communauté Steam   [SS_GM]Mardan-CrunchyInTheory.htm" and clicking on the image.

Comment 4

[Boris Zbarsky [:bzbarsky]]

jdm, do you own this srcset stuff now?

Comment 5

[Josh Matthews [:jdm]]

More or less, yeah.

Comment 6

[Josh Matthews [:jdm]]

It's fascinating that the iframe makes a difference here. I can reproduce; thanks for the great testcase, Loic!

Comment 7

[Loic]

My testcase works only at the 1st load, you have to reload the page to reproduce the issue, but I guess it's the same underlying bug, even if it's reproducible on every call of the modal iframe on Steam (probably due to more complex JS stuff).

Comment 8

[Josh Matthews [:jdm]]

Turns out this is bug 1166138. The presence of the `display: none` on the iframe is the key here - when I add <picture></picture> around the img, the testcase works as expected. Since there's no viewport when the image selection first occurs, we bail and try to load an empty URL string. With a picture element, we correct notice when the element first gets a viewport and re-run the image selection at that point.