LM20.1 WebApps won't work properly with Vivaldi Browser

[slartyblartfast]

When the new Web Apps is launched using my default browser, Vivaldi, it opens only in full screen mode. When I attempt to reduce the display to a desktop window, it shuts down the app. Web Apps appears to work properly with Firefox including "windowing" the display.

I couldn't find any other place to register this error.

Dell E6510 laptop on a PRO3X port extender.