1804098 - Two white lines are displayed on the progress bar of the “about:welcome” page when there are six screens

Status: VERIFIED FIXED

(Firefox :: Messaging System, defect)

Description

[Simona Rosu [:srosu], Ecosystem QA]

Attachment: ProgressBar_WhiteLines.png

[Affected versions]:

• Firefox Nightly 109.0a1 (Build ID: 20221204094021)

[Affected Platforms]:

• Windows 10 x64
• macOS 11.7.1
• Ubuntu 22.04 x64

[Prerequisites]:

• Have the latest version of the Firefox Nightly build installed and opened.
• Have the Firefox browser not pinned to the Taskbar and not set as default.

[Steps to reproduce]:

1. Open the browser with the profile from the prerequisites.
2. Navigate to the "about:welcome" page.
3. Navigate through the "Onboarding" screens until the last screen is displayed.
4. Observe the progress bar.

[Expected result]:

• The progress bar is correctly displayed.

[Actual result]:

• Two unnecessary lines are displayed on the progress bar.

[Regression Window]:

• The issue is not reproducible with older Nightly 109.0a1 builds. Considering this using mozregression tools I have found the regression range. Here are the results:
  Last good revision: 2af51023c5830f0a6d57c1d07de92727b85af599
  First bad revision: cdf07ffca6205f336682391ffd8d349ea4935f65
  Pushlog: link

From this pushlog it seems that Bug 1794702 may have introduced this behavior.

[Notes]:

• This issue is not reproducible when the Onboarding contains 5 screens.
• Attached is a screenshot of the issue.

Comment 1

[Simona Rosu [:srosu], Ecosystem QA]

Hi @Shane, could you please take a look over this issue?

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1794702

Comment 3

[Shane Hughes [:aminomancer]]

Hi Simona just out of curiosity, is WebRender enabled?

There's a rule that's supposed to prevent these kinds of subpixel discrepancies, though apparently it doesn't always work. With my 1.5x scaling factor, I'm able to reproduce it by zooming the page to 120%. Probably best to just add a negative margin between them so any subpixel discrepancies fall into that wiggle room

Comment 4

[Shane Hughes [:aminomancer]]

Attachment: Bug 1804098 - Avoid subpixel rounding inconsistencies in about welcome progress bar. r=negin

Comment 5

[Simona Rosu [:srosu], Ecosystem QA]

@Shane, I have Webrender enabled on the latest Nightly.

Comment 6

[Shane Hughes [:aminomancer]]

(In reply to Simona Rosu [:srosu], Ecosystem QA from comment #5)

@Shane, I have Webrender enabled on the latest Nightly.

Great thanks for letting me know. I won't be able to fix the WebRender scaling issue myself but I think we have a solid workaround.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c70f25c82e27
Avoid subpixel rounding inconsistencies in about welcome progress bar. r=negin

Comment 8

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/c70f25c82e27

Comment 9

[Simona Rosu [:srosu], Ecosystem QA]

I‘ve verified this issue using the latest Firefox Nightly 109.0a1 (Build ID: 20221208094253) on Windows 10 x64, macOS 11.7.1, and Ubuntu 22.04 x64.

• No subpixels are visible on the progress bar of the “about:welcome” page.