An element that went fullscreen gets the screen and the fullscreen display mode
After requestFullscreen() resolves, display-mode is 'fullscreen' and the outer window covers the screen to within a pixel. N/A when the request is rejected, on Brave and on non-Chromium engines (severity: warn).
What a detector infers
When a page calls requestFullscreen() during a click, Chrome normally makes the whole window fullscreen: document.fullscreenElement is set, the window grows to cover the screen, and the display-mode media query switches to 'fullscreen'. There is one deliberate exception.
If the tab is being visibly captured — shared in a video call, say — Chrome keeps the fullscreen inside the tab so the shared picture keeps its size: fullscreenElement is set, but the window does not change and display-mode stays 'browser'. Playwright's focus emulation registers itself with Chrome as exactly such a visible capture, so under Playwright, headed or headless, every requestFullscreen goes into the tab.
Measured: genuine headed Chrome, clicked through the DevTools protocol directly, reached display-mode 'fullscreen' with the outer window equal to the screen; Playwright got fullscreenElement with display-mode 'browser' and the window unchanged. The audit requests fullscreen inside the Run click and exits at once. A rejected request is N/A, as are non-Chromium engines and Brave, which varies screen geometry as a privacy feature.
The one ordinary way to produce the failing shape is to run the audit in a tab that is being shared at that moment.
How to resolve it
The within-tab routing comes from a capture that the automation client's focus emulation registers, not from the page. Drive the browser through a client that does not enable focus emulation, or expect fullscreen requests to stay inside the tab under one that does.
Nearby checks in Screen & display
- A desktop browser does not expose touch-event feature detection
desktop-has-no-touch-eventsWhether 'ontouchstart' in window is true is not decided by the hardware. - A frameless window covering its screen is in fullscreen display mode
frameless-covering-is-fullscreenA desktop browser window has a frame — tab strip, toolbar, borders — so its outer size is larger than its viewport. - devicePixelRatio is the scale layout actually rasterises at
dpr-vs-device-pixelsdevicePixelRatio is meant to be the scale at which layout is rasterised, and several parts of the browser act on the real scale rather than… - Pointer coordinates agree with the window's own position
event-coords-vs-window-geometryA pointer event carries viewport coordinates (clientX/Y) and screen coordinates (screenX/Y), and the browser derives the second from the… - screen.width/height backed by the display (matchMedia)
screen-matchmediaThis check reads window.screen.width/height, then asks the CSS media-query engine the same question via matchMedia("(device-width: Npx) and… - devicePixelRatio matches matchMedia resolution
dpr-matchmediaThe check compares window.devicePixelRatio against the layout engine's own answer, querying matchMedia with a min-resolution/max-resolution… - The screen times devicePixelRatio is a panel a monitor actually has
dpr-screen-vs-panelOn Windows, screen.width and screen.height are reported in scaled pixels — the physical panel divided by the display scale — and at 100%… - Screen dimensions are a plausible physical size
screen-plausibleA pure sanity range on screen.width and screen.height: both must be at least 200px and no more than 16384px.
Clearcote is a browser built for fingerprint coherence
It is a Chromium fork, maintained by the same people who wrote this reference. It ships as a compiled browser rather than as a stealth script injected into someone else's — which is a description of how it is built, and is not an argument about how it behaves on this check.
This audit takes no position on how Clearcote scores on Screen & display checks, on this one, or anywhere else. It has no baseline corpus of other people's fingerprints to rank you against and no vendor scoreboard — nearly every check is self-referential, asking one browser the same question through two independent APIs and reporting whether both answers can be true at once. It runs identically on any browser, including ours. Run it on yours and read the result yourself.
See the other checks in Screen & display — the family fullscreen-is-real-fullscreen belongs to.