Open Bug 2031465 Opened 1 month ago Updated 9 days ago

White flash on startup caused by abouthome_cache storing incompatible startup frame

Categories

(Firefox :: New Tab Page, defect)

Product:
Firefox
Component:
New Tab Page
Version:
Firefox 150
Platform:
Desktop
Windows 11
Type:
defect

Tracking

()

Status:
UNCONFIRMED

People

(Reporter: klaydyeu, Unassigned, NeedInfo)

Details

Steps to reproduce:

  1. Install Firefox 149.0.2 on Windows 11
  2. Launch Firefox and wait — Remote Settings automatically installs newtab@mozilla.org version 151.2.20260328 via rollout "New Tab 151.2.20260328.211913 to Release 149"
  3. Restart Firefox

Expected result:
Firefox opens smoothly without visual artifacts

Actual result:
Screen flashes white for ~1 second during startup, before the UI finishes rendering

Additional info:

  • Reproduces on any profile, including a brand new clean profile with no account and no customizations
  • The rollout is visible in about:support under "Remotely Enabled Features": "New Tab 151.2.20260328.211913 to Release 149 (rollout)"
  • newtab@mozilla.org version 151.2.20260328.211913 installed via app-profile (not app-builtin)
  • Without the rollout the flash does not occur
  • Tested on: Firefox 149.0.2, Windows 11 build 26200, NVIDIA GeForce GTX 1070 Ti, driver 32.0.15.8228

Update after additional testing on Firefox 150.0:

On Firefox 149, the rollout "New Tab 151.2.20260328.211913 to
Release 149" was delivered via Remote Settings after first launch.
On Firefox 150, it is present by default on all clean profiles
without any Remote Settings sync needed.

Root cause chain:

  1. Fresh Firefox install - no flash on very first launch
    (abouthome_cache not yet created)
  2. After first launch, abouthome_cache stores a startup frame
  3. Every subsequent launch shows white flash from this cached frame

Key finding: the bug is fully resolved by setting
browser.startup.homepage.abouthome_cache.enabled to false,
confirming abouthome_cache as the exact delivery mechanism
of the visual artifact.

Note: the rollout "New Tab 151.2.20260328.211913 to Release 149"
was observed on all tested profiles in both Firefox 149 and 150.
Its connection to the bug is unclear but worth investigating.

OS: Unspecified → Windows 11
Hardware: Unspecified → Desktop
Summary: White flash on startup caused by Remote Settings rollout of New Tab 151.2.20260328 on Firefox 149 → White flash on startup caused by abouthome_cache storing incompatible startup frame
Version: Firefox 149 → Firefox 150

The severity field is not set for this bug.
:thecount, could you have a look please?

For more information, please visit BugBot documentation.

Flags: needinfo?(sdowne)

Just to clarify: this issue is highly visible and extremely disruptive specifically when using Dark Theme / Dark Mode. The white cached frame acts like a flashbang against the dark UI

This issue reproduces on every startup and disproportionately affects users running system-wide dark themes. The full-screen white cached frame creates a high-contrast flash that is visually aggressive and impacts accessibility and perceived startup quality

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