2046010 - 487.6 - 43.2% buzzfeed LastVisualChange + 2 more (Linux) regression on Wed June 3 2026

Status: RESOLVED FIXED

(Core :: DOM: Service Workers, defect, P2)

Description

[Treeherder Bug Filer]

Perfherder has detected a browsertime performance regression from push 2b451e361b7f820e8423972ca41757e670cfcc0c. As author of one of the patches included in that push, we need your help to address this regression.

Please acknowledge, and begin investigating this alert within 3 business days, or the patch(es) may be backed out in accordance with our regression policy.

Regression	Test	Platform	Options	Absolute values [old vs new]	Performance Profiles
488%	buzzfeed LastVisualChange (doc)	linux2404-64-shippable	fission warm webrender	813.46 -> 4,779.85	Before/After
336%	buzzfeed LastVisualChange (doc)	linux2404-64-shippable	cold fission webrender	1,105.75 -> 4,822.22	Before/After
43%	fandom LastVisualChange (doc)	linux2404-64-shippable	fission warm webrender	248.73 -> 356.19	Before/After

Improvements	Test	Platform	Options	Absolute values [old vs new]	Performance Profiles
59%	buzzfeed fcp (doc)	linux2404-64-shippable	cold fission webrender	536.65 ms -> 219.78 ms	Before/After
58%	buzzfeed largestContentfulPaint (doc)	linux2404-64-shippable	cold fission webrender	708.54 ms -> 297.78 ms	Before/After
56%	fandom largestContentfulPaint (doc)	linux2404-64-shippable	fission warm webrender	100.16 ms -> 43.82 ms	Before/After
55%	buzzfeed ContentfulSpeedIndex (doc)	linux2404-64-shippable	cold fission webrender	743.89 ms -> 335.97 ms	Before/After
50%	buzzfeed FirstVisualChange (doc)	linux2404-64-shippable	cold fission webrender	570.20 ms -> 287.62 ms	Before/After
...	...	...	...	...	...
20%	buzzfeed loadtime (doc)	linux2404-64-shippable	fission warm webrender	903.98 ms -> 726.14 ms	Before/After

Support & Actionable Steps

For questions, please contact [e-mail]. You can also find help on Slack (#perf-help) or Matrix (#perftest).

Action guide details:

• See the guide to handling regression bugs for investigation steps.
• Review the alert summary for affected tests, graphs, and comparisons.
• Check the PerfCompare results.
• Tests on Try: Run all tests using ./mach try perf --alert 50657 (See documentation link for details).
• Profiling jobs: Trigger jobs from Treeherder job view or request them from [e-mail].

Comment 1

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

Set release status flags based on info from the regressing bug 1201160

Comment 2

[Eden Chuang[:edenchuang]]

It is somehow a reasonable situation after backing out the patch of bug 1201160.

After back out the patch of 1201160, the nocors cross-origin style fetching will be intercepted by ServiceWorker. It is reasonable to take time to launch ServiceWorker and handle the CSS fetch. Especially if ServiceWorker just falls back or times out the fetch event handler.

What the actual fix for bug 1201160 would be implemented in bug 2029029. If possible, I would like to revisit the performance problem after the patches in bug 2029029 are landed.

Comment 3

[Dianna Smith [:diannaS]]

Marked as fixed by backout for 152, 153.