Fullscreen tab/address bar should overlay content instead of shrinking viewport (like Edge/Chrome)

When using Firefox in fullscreen mode (via F11) on Windows or Linux, moving the mouse to the top reveals the tab and address bar. but this causes the page content below to shrink temporarily. In comparison, Chromium-based browsers handle this differently: their tab and address bars appear as overlays, without disturbing the layout or causing any viewport resize. This results in a more immersive and fluid fullscreen experience. Please consider implementing a similar overlay behavior in Firefox's fullscreen mode, or at least providing a toggle via about:config to allow users to choose between current behavior and overlay-style tab reveal.