How can an agent resolve this problem? [Bug]: default font families are lost after any screenshot captured beyond the viewport (Chromium headless shell)
Finding: In an external report on Playwright 1.63.0 with the bundled Chromium headless shell 153.0.8010.12, the first screenshot captured beyond the viewport (fullPage) makes the generic font families (sans-serif, serif, monospace, cursive, fantasy) resolve to different fonts than the ones Playwright set, and the page is laid out again (https://github.com/microsoft/playwright/issues/42962). This is an external report only; KFA did not reproduce it.
Reported conditions: on macOS arm64 the reporter saw sans-serif move from Helvetica-Bold to Arial-BoldMT, and the last line shifted from 1960px to 1999px. On Ubuntu 24.04 in Docker (arm64) only monospace changed, from WenQuanYiZenHeiMono to LiberationMono-Bold. A viewport-only screenshot did not trigger it, and a navigation restored Playwright's families until the next beyond-viewport capture (issue body, https://github.com/microsoft/playwright/issues/42962). A commenter reported a similar Linux effect on Playwright Python 1.56.0 with Chromium 141, where monospace resolved to Liberation Mono instead of DejaVu Sans Mono (https://github.com/microsoft/playwright/issues/42962#issuecomment-6013695685). Another commenter reported the same on macOS arm64 with 1.63.0, plus a parallel-suite case where page height alternated between 30049 and 30083 across toHaveScreenshot captures until a stability timeout. They could not trigger the reverse switch on demand (https://github.com/microsoft/playwright/issues/42962#issuecomment-6088861148).
Cause status: the reporter hypothesizes that Page.captureScreenshot with captureBeyondViewport pushes WebPreferences, which overwrites the fonts set by Page.setFontFamilies. Raw CDP tests on the same page point to captureBeyondViewport alone as the trigger: a 1x1 clip with it changed fonts, the same command without it did not, and a viewport resize and restore did not. No maintainer has confirmed the cause in the supplied data.
Mitigations reported by commenters (not verified by KFA): resize the viewport to the page height, take a normal screenshot, then restore the viewport, which avoids captureBeyondViewport but affects vh units and media queries; or send Page.setFontFamilies on a CDP session kept attached for the page's life, which reportedly survives navigations.
Fix status: the issue is open, and no fix commit or released fix is supplied. Results vary by platform, and the reverse switch was intermittent.
Problem details
- Observed symptom
- After the first beyond-viewport screenshot, generic font families resolve to different fonts and the page is laid out again. Viewport-only screenshots do not trigger it. A navigation restores Playwright's families until the next such screenshot.
- Context
- Chromium headless default font families and captureBeyondViewport screenshots; Reported on Playwright 1.63.0 with Chromium headless shell 153.0.8010.12 (macOS arm64; Linux arm64 in Docker). A commenter also reported Playwright Python 1.56.0 with Chromium 141 on Linux.; page.screenshot with fullPage: true (Page.captureScreenshot with captureBeyondViewport) after Playwright sets default font families; External reports only; not reproduced by KFA.; Results are platform dependent: on Linux only monospace changed, on macOS all generic families changed.; The CDP/Chromium internals cause is the reporter's analysis, not maintainer-confirmed.; The workarounds come from non-maintainer commenters and are untested here; the resize workaround alters layout-dependent pages.; The second commenter saw an intermittent reverse switch in parallel runs that they could not trigger on demand.; The thread may omit middle comments, and the related issues cited by the reporter were not supplied.; One commenter disclosed commercial interest.
- Environment
- State
- partial
- Text
- Reported on Playwright 1.63.0 with Chromium headless shell 153.0.8010.12 (macOS arm64; Linux arm64 in Docker). A commenter also reported Playwright Python 1.56.0 with Chromium 141 on Linux.; source-reported environment only
- Symptom signature
- Literal source
- Not supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 2
Reported mitigations: pin the fixed font family on a retained CDP session (macOS) or resize before capture (Linux); not verified by KFA
Source-backed, not verified by KFA. Two commenters with no repository association (author_association NONE) each reported a different workaround on https://github.com/microsoft/playwright/issues/42962, each on a single platform and version. The supplied thread does not describe either as a maintainer-confirmed fix. The supplied thread coverage is partial (head/tail) and may omit maintainer or other comments.
1) Retained-session font pin, reported on macOS arm64 with Playwright 1.63.0 and Chromium headless shell 153.0.8010.12. This commenter reported pinning only the fixed (monospace) family to Menlo via Page.setFontFamilies, sent once per page before the first navigation, on a CDP session kept attached for the page's life. They said later beyond-viewport captures stayed byte-identical, and that an override sent on a session later detached was lost at the next navigation (https://github.com/microsoft/playwright/issues/42962#issuecomment-6088861148). Only the fixed family was pinned; other families were not reported. The same commenter separately reported an intermittent reverse font switch in a 6-worker parallel toHaveScreenshot suite that they could not trigger on demand. They did not state whether the pin was applied in that suite, so the pin's behavior there is unknown.
2) Viewport resize, reported on Linux with Playwright Python 1.56.0 and Chromium 141 headless shell; no CPU architecture was stated. That commenter observed monospace resolving to Liberation Mono instead of DejaVu Sans Mono after a full-page screenshot. They then resized the viewport to the scroll height, took a regular screenshot and restored the viewport. In their single test the fonts stayed the same, also after restoring the viewport; they did not state which families they checked. They warned this alters vh units and media queries and was not tested on such pages (https://github.com/microsoft/playwright/issues/42962#issuecomment-6013695685). Other platform and version combinations are untested. This commenter disclosed commercial interest in the area.
- Problem id
- 140b70fe-69eb-46ad-8ece-14b258462e28
- Proposed action
- Reported by commenters, not verified by KFA. (a) On macOS arm64, Playwright 1.63.0, Chromium headless shell 153.0.8010.12: the commenter sent Page.setFontFamilies pinning only fixed: 'Menlo' once per page before the first navigation and kept that CDP session attached for the page's lifetime. (b) On Linux, Playwright Python 1.56.0, Chromium 141 (architecture not stated): the commenter resized the viewport to the page height, took a normal screenshot, then restored the viewport. Other combinations are untested.
- Applicability
- State
- partial
- Text
- Retained-session setFontFamilies pin: reported on macOS arm64 with Playwright 1.63.0 and Chromium headless shell 153.0.8010.12. Resize workaround: reported on Linux with Playwright Python 1.56.0 and Chromium 141; architecture not stated. Neither was reported on other combinations, which are untested.
- Limitations
- State
- known
- Text
- External reports only; not reproduced by KFA. Each workaround rests on a single commenter report. The issue reporter's own results (not the workaround commenters') were that on Linux arm64 in Docker only monospace changed, and on macOS all generic families changed. The CDP/Chromium internals cause is the issue reporter's analysis, not maintainer-confirmed. The resize workaround may alter layout-dependent pages (vh units, media queries), untested there. The macOS arm64 commenter (comment 6088861148) reported an intermittent reverse switch in parallel runs that they could not trigger on demand and did not say whether the pin was applied in that suite. The supplied thread may omit middle, maintainer or other comments, and related issues cited by the reporter were not supplied. The Linux resize commenter (comment 6013695685) disclosed commercial interest.
- Success criteria
- Unknown · not established
- Risk notes
- State
- partial
- Text
- Resizing the viewport can change vh-based and media-query layout. Only the fixed family was pinned in the reported pin workaround, and a detached session loses the override at the next navigation.
- Lifecycle
- active
Page 1 · 1 children total
Sources and related records
No source relations recorded.