feat(firefox): roll to r1551

[microsoft-playwright-automation]

Browser build: https://github.com/microsoft/playwright-browsers/commit/1b6b3bfd70df382bddfff8a5605c5b4606b32272. Build has full platform coverage - check that all tests pass there.

[github-actions]

Test results for "tests 1"

6 flaky

⚠️ [chromium-library] › library/chromium/chromium.spec.ts:213 › should intercept service worker requests (main and within) `@chromium-ubuntu-22.04-node20`
⚠️ [chromium-library] › library/video.spec.ts:690 › screencast › should capture full viewport `@chromium-ubuntu-22.04-node22`
⚠️ [chromium-library] › library/video.spec.ts:725 › screencast › should capture full viewport on hidpi `@chromium-ubuntu-22.04-node22`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:257 › third party 'Partitioned;' cookies `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:470 › top level 'Partitioned;' cookie and same origin iframe `@firefox-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:827 › should update state on subsequent run `@windows-latest-node22`

52039 passed, 1244 skipped

---

Merge workflow run.

[github-actions]

Test results for "MCP"

1 failed
❌ [firefox] › mcp/cli-session.spec.ts:54 › idle timeout shuts the session down @mcp-windows-latest-firefox

8691 passed, 1474 skipped

---

Merge workflow run.

[github-actions]

Hi, I'm the Playwright bot and I triaged the CI failures on this PR.

🟢 The one failure is a known pre-existing flake — this PR is clear

[firefox] › mcp/cli-session.spec.ts:54 › idle timeout shuts the session down fails on mcp-windows-latest-firefox regardless of what's being tested: 44 of 143 runs red (31%), 99 green, including plain pushes to main.

Details

The roll itself touches browser_patches/firefox/juggler/NetworkObserver.js (response header reading), juggler/content/main.js (per-process channel id), and the Firefox revision bump to r1551. Nothing in the MCP CLI session lifecycle path. The rest of CI is green — 52039 passed in "tests 1", 8691 in "MCP", with 6 flaky results that resolved on retry.

Pre-existing flake / infra

• [firefox] › mcp/cli-session.spec.ts:54 › idle timeout shuts the session down @mcp-windows-latest-firefox — fails only on this one bot; every other MCP bot (12 of them, including mcp-ubuntu-latest-firefox and mcp-macos-latest-firefox) is 100% green across ~150 runs each, so it isn't the Firefox build. The same assertion fails on SHAs this PR can't be responsible for, e.g. main at b8627f95, f14e9f5c, dc82cd77, and unrelated PRs fix(chromium): report 204 subresource responses as finished #42834 (fix-42786), docs(cli): do not suggest generating test scenarios in parallel #42833, fix(firefox): preserve response header field boundaries #42832, chore(coverage): istanbul instrumentation for the trace viewer and html reporter #42785.

  Always the same signature — the session list hasn't emptied yet when the assertion runs:

  expect(received).toContain(expected)
  Expected substring: "(no browsers)"
  Received string:    "#…"
  

  Last 40 runs on that bot, oldest first:

  🟩🟩🟥🟩🟥🟥🟥🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟥🟩🟩🟩🟥🟩🟩🟥🟩🟩🟩🟥🟩🟥🟩🟥🟩🟩🟩🟩🟩🟥

_{Triaged by the Playwright bot - agent run}

[github-actions]

Test results for "tests 2"

39 failed
❌ [chromium-library] › library/coverage.spec.ts:34 › should collect istanbul coverage into the trace @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:55 › should collect coverage per trace chunk @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:81 › should report maps once and counters incrementally @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:109 › should accumulate counters across pulls and keep never hit files @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:135 › should collect coverage of a page closed by in-page script @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:157 › should not double count a stash picked up twice @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:179 › should discard stashes of other sessions @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:199 › should collect coverage of an origin left without a page @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:229 › should pull counters as the actions go @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:246 › should not collect coverage without the option @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:259 › should count only the hits after start @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:276 › should stop collecting when tracing stops @tracing-chromium
❌ [chromium-library] › library/coverage.spec.ts:293 › should surface a failure to stash the coverage @tracing-chromium
❌ [firefox-library] › library/coverage.spec.ts:34 › should collect istanbul coverage into the trace @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:55 › should collect coverage per trace chunk @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:81 › should report maps once and counters incrementally @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:109 › should accumulate counters across pulls and keep never hit files @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:135 › should collect coverage of a page closed by in-page script @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:157 › should not double count a stash picked up twice @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:179 › should discard stashes of other sessions @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:199 › should collect coverage of an origin left without a page @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:229 › should pull counters as the actions go @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:246 › should not collect coverage without the option @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:259 › should count only the hits after start @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:276 › should stop collecting when tracing stops @tracing-firefox
❌ [firefox-library] › library/coverage.spec.ts:293 › should surface a failure to stash the coverage @tracing-firefox
❌ [webkit-library] › library/coverage.spec.ts:34 › should collect istanbul coverage into the trace @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:55 › should collect coverage per trace chunk @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:81 › should report maps once and counters incrementally @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:109 › should accumulate counters across pulls and keep never hit files @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:135 › should collect coverage of a page closed by in-page script @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:157 › should not double count a stash picked up twice @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:179 › should discard stashes of other sessions @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:199 › should collect coverage of an origin left without a page @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:229 › should pull counters as the actions go @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:246 › should not collect coverage without the option @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:259 › should count only the hits after start @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:276 › should stop collecting when tracing stops @tracing-webkit
❌ [webkit-library] › library/coverage.spec.ts:293 › should surface a failure to stash the coverage @tracing-webkit

31 flaky

⚠️ [chromium-library] › library/client-certificates.spec.ts:878 › browser › support http2 if the browser only supports http1.1 `@msedge-dev-windows-latest`
⚠️ [chromium-library] › library/chromium/chromium.spec.ts:436 › should produce network events, routing, and annotations for Service Worker (advanced) `@chrome-ubuntu-22.04`
⚠️ [chromium-library] › library/video.spec.ts:762 › screencast › should work with video+trace `@chromium-windows-latest`
⚠️ [chromium-library] › library/chromium/oopif.spec.ts:179 › should take screenshot `@chromium-macos-15-xlarge`
⚠️ [chromium-library] › library/trace-viewer-scrub.spec.ts:226 › should reveal snapshot when hovering an action or picking a locator during playback `@chrome-beta-ubuntu-22.04`
⚠️ [chromium-library] › library/selector-generator.spec.ts:70 › selector generator › should not escape spaces inside named attr selectors `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:280 › selector generator › should not use generated id `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:323 › selector generator › should use parent text `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:412 › selector generator › should not use input[value] `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:551 › selector generator › should accept valid aria-label for candidate consideration `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:617 › selector generator › should generate exact title when necessary `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:641 › selector generator › should generate exact label when necessary `@chrome-macos-latest`
⚠️ [chromium-library] › library/selector-generator.spec.ts:683 › selector generator › should generate noText: name from aria-label `@chrome-macos-latest`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:257 › third party 'Partitioned;' cookies `@tracing-firefox`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:470 › top level 'Partitioned;' cookie and same origin iframe `@tracing-firefox`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:257 › third party 'Partitioned;' cookies `@firefox-macos-15-large`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:470 › top level 'Partitioned;' cookie and same origin iframe `@firefox-macos-15-large`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:257 › third party 'Partitioned;' cookies `@firefox-windows-latest`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:470 › top level 'Partitioned;' cookie and same origin iframe `@firefox-windows-latest`
⚠️ [firefox-library] › library/signals.spec.ts:25 › should close the browser when the node process closes `@firefox-windows-latest`
⚠️ [firefox-library] › library/browsercontext-basic.spec.ts:170 › should make a copy of default viewport `@firefox-macos-15-xlarge`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:257 › third party 'Partitioned;' cookies `@firefox-macos-15-xlarge`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:470 › top level 'Partitioned;' cookie and same origin iframe `@firefox-macos-15-xlarge`
⚠️ [firefox-library] › library/har.spec.ts:109 › should populate entry startedDateTime from the browser `@firefox-macos-15-xlarge`
⚠️ [webkit-library] › library/trace-viewer-scrub.spec.ts:196 › should show screencast while playing and snapshot when stopped `@webkit-macos-15-xlarge`
⚠️ [webkit-library] › library/trace-viewer-scrub.spec.ts:256 › should show screencast while dragging and snap to the action on release `@webkit-macos-15-xlarge`
⚠️ [webkit-library] › library/trace-viewer.spec.ts:1997 › canvas clipping `@webkit-macos-15-xlarge`
⚠️ [webkit-library] › library/tracing.spec.ts:533 › should produce screencast frames fit `@webkit-macos-15-xlarge`
⚠️ [webkit-library] › library/browsertype-connect.spec.ts:813 › launchServer › should upload a folder `@webkit-macos-15-large`
⚠️ [android-page] › page/page-goto.spec.ts:460 › should disable timeout when its set to 0
⚠️ [android-page] › page/page-request-fulfill.spec.ts:81 › should fulfill with unuassigned status codes

112008 passed, 4738 skipped

---

Merge workflow run.

[github-actions]

Hi, I'm the Playwright bot and I triaged the CI failures on this PR.

🟢 All 39 failures are pre-existing — this PR is clear

Every failure is library/coverage.spec.ts on the @tracing-* bots, all 13 tests × chromium, firefox and webkit, with the same error: Error: tracing.start: Tracing has been already started. That file has never passed on a tracing bot since it landed — 0 green in ~40 runs per bot, on main and on unrelated PRs.

Details

The roll touches browser_patches/firefox/juggler/NetworkObserver.js, juggler/content/main.js and the Firefox revision bump to r1551 — Firefox-only, so it can't explain the identical chromium and webkit failures.

Pre-existing flake / infra

• [chromium-library|firefox-library|webkit-library] › library/coverage.spec.ts:34,55,81,109,135,157,179,199,229,246,259,276,293 @tracing-chromium / @tracing-firefox / @tracing-webkit — 100% red on those bots since the file first appeared on 2026-09-11, including plain pushes to main (2a095f6f, b8627f95, 9f6e40f0, e2f94e3f, f14e9f5c, 07f1a615, d16ccf0c) and unrelated PRs chore(deps): bump the github-actions group with 2 updates #42824 (dependabot) and feat(chromium): roll to r1246 #42757 (roll-into-pw-chromium/1246). Not a flake — a permanently broken combination: the tracing bots start tracing from a fixture, and the test calls tracing.start() again.

  tracing-firefox, last 20 runs, oldest first:

  🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥

The other two reports on this PR are clean apart from retried flakes: "tests 1" is green (52039 passed, 6 flaky), and "MCP" has the one already-known mcp/cli-session.spec.ts:54 › idle timeout shuts the session down failure on @mcp-windows-latest-firefox, which flips verdict on unrelated SHAs too.

_{Triaged by the Playwright bot - agent run}