Steps to reproduce:

Running ./mach test browser/components/resistfingerprinting/test/browser/browser_roundedWindow_* --setpref=widget.wayland.vsync.enabled=true on Gnome Wayland or Plasma Wayland.

widget.wayland.vsync.enabled=true is the default setting. With vsync disabled widget.wayland.vsync.enabled=false this problem does not exist. The problem only exists since https://phabricator.services.mozilla.com/D155385 from Bug 1786513.

Actual results:

New windows fail at becoming the specified size early enough after window.open(someUrl, "", "width=200,height=200") calls. At the time of the load event innerWidth and innerHeight still match the size set by AppWindow::ForceRoundedDimensions instead of the size set by SizeOpenedWindow from nsWindowWatcher.cpp.

Expected results:

Independent of vsync settings new windows should, at the time of the load event, already have become the size specified in the window.open call.

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Gtk' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.