Safari intermittently displays a white flash when opening a new tab overridden by a web extension.
I reproduced this on an iPhone 13 mini running iOS 26.5 using a minimal test extension.
The extension replaces the new tab page through chrome_url_overrides.newtab. The page has a static magenta background, set directly on the root element and through inline CSS.
The test page contains no JavaScript, images, fonts, external stylesheets or network requests.
- Install and enable a Safari Web Extension that overrides the new tab page with a static magenta HTML page.
- Select the extension for new tabs in Safari settings.
- Open Safari in normal browsing mode.
- Open a new tab and wait for the magenta page to appear.
- Open another new tab.
- Repeat several times.
Expected: The page area remains magenta throughout the transition.
Actual: The page area intermittently transitions from magenta → white → magenta.
The issue reproduces without JavaScript or external resources, so the flash does not require delayed script execution or image loading.
Is this a known issue with Safari’s handling of new tab overrides? Is there a supported way for an extension to control the background displayed during this transition?
Thanks for the minimal reproduction. A static page with no script or external resources isolates this well.
I reproduced it on an iPhone 18 Pro Max with iOS 27.0, using a static magenta new tab page. A screen recording shows Safari's toolbar over a blank page area for one to three frames, about 17 to 50 milliseconds, before the extension's page appears. The blank area is white in Light Mode and black in Dark Mode. It happened most often with New Tab in the menu that appears when you touch and hold the tabs button. It also happened occasionally from the tab overview.
I didn't find a documented way for an extension to control what Safari shows during that transition. The theme-color meta tag colors Safari's tab bar, as Explore Safari Web Extension improvements describes, but not the page area.
Please consider filing a bug report about this so our engineering teams can investigate this issue. Include your minimal extension and a screen recording that shows the flash. A resolution may involve changes to Apple's software. If you post the Feedback number here I'll check the status next time I do a sweep of forums posts where I've suggested bug reports.
Bug Reporting: How and Why? has tips on creating your report.