React.lazy, Suspense and the Hidden 300 ms Delay

The team behind the Tab Widgets extension found that React's 300 ms reveal throttle, not bundle size, delayed its dashboard. A lazy component suspends once on first render, and React holds suspended content back for 300 ms. Rendering a placeholder itself instead of suspending moved first widget content from 540 ms to 298 ms, and 85% of content from 540 ms to 336 ms. Full load was unchanged. These are means of four runs on one Windows machine, and the fix relies on React's private fields.