Comment 76 for bug 1953685

(In reply to Martin Stránský [:stransky] (ni? me) from comment #72)
> And where the connection happens?

I'd have to dive into bug 1645528 again to remember all the details but IIRC once the content process creates a `BrowserChild`, a `BrowserParent` is created, which again, at least on Wayland, has a `VsyncParent` (the `BrowserChild` has a `VsyncChild`). That `VsyncParent` calls `GetVsyncSource()` on its Widget - in the case here the `nsWindow`.
Normally, if a tab gets moved to another window, the `VsyncSource` of the `VsyncParent` should get updated, but maybe that's not the case if the global software vsync source is selected.
In any case, what we see here is a race between a `VsyncParent` and the `WaylandVsyncSource` being created.