White flash when opening a new tab overridden by a Safari Web Extension on iOS 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. Minimal reproduction 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. Steps to reproduce 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?