2028958 - The latest version of Firefox Developer Edition seems to have a CSS rendering issue

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Rin]

Attachment: Example of the visual issue in Firefox Developer Edition 150.0b4

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:149.0) Gecko/20100101 Firefox/149.0

Steps to reproduce:

Reproduction

https://github.com/TurtIeSocks/firefox-dev-bg-render-issue

The reproduction was created with a simple Bun+Vite+React app, but I first experienced this on a NextJS based app.

System Information

MacBook Pro 14in Nov 2024
Apple M4 Pro
macOS Tahoe 26.2

I apologize if this is under the wrong product or has already been reported. I did not see a product listing specifically for Firefox Developer Edition.

Actual results:

After updating my Firefox Developer Edition to the latest version (150.0b4 aarch64) I noticed an unusual CSS rendering issue that was not present in the previous version.

Unfortunately, I did not record which version I was on prior to updating.

I'm not deeply familiar with the inner working of CSS so I'm not sure what the correct technical phrases are to describe what is happening other than, it's not rendering what was being rendered in the previous version that my Firefox DE was on or in the latest versions of many other popular browsers. The screenshot and reproduction project do a better job of describing the visual issue.

Expected results:

I would expect that CSS/HTML in Firefox Developer Edition would render (roughly) the same result as standard Firefox, Chrome, and Safari.

Browsers without the Rendering Issue

• Safari 26.2
• Firefox (non Developer Edition) 149.0
• Chrome Canary 148.0.7768.0

Comment 1

[Emilio Cobos Álvarez [:emilio]]

[Tracking Requested - why for this release]: Very visible rendering regression

Thanks! I can repro and I could minimize this further.

Mozregression says this comes from: https://hg-edge.mozilla.org/integration/autoland/pushloghtml?fromchange=e5b8d114814786a5ca7ce15acca96a0ae08fd079&tochange=88630521422d2b08d2164f742cc6206889d78511

Nical, can you take a look? Not sure which one is the right regressing bug of those three.

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Reduced test-case.

Comment 3

[BugBot [:suhaib / :marco]]

The bug is marked as tracked for firefox150 (beta). However, the bug still isn't assigned.

:bhood, could you please find an assignee for this tracked bug? Given that it is a regression and we know the cause, we could also simply backout the regressor. If you disagree with the tracking decision, please talk with the release managers.

For more information, please visit BugBot documentation.

Comment 4

[Dianna Smith [:diannaS]]

is there an update for 150 for this? we are in RC week.

Comment 5

[Nicolas Silva [:nical]]

This appears to have been fixed, presumably by one of the many patches I landed and uplifted last week. I'll close the bug but feel free to reopen if I missed anything.