function checkVivaldi(wnd) {
  if (wnd.vivExtData/*new*/ || wnd.extData/*old*/) {
    setBrowserName('Vivaldi');
  }
}
@type {number|void} DANGER! Until init is done the only sure thing about this value
is whether it's truthy, because UA can be overridden by about:config.
Using `void` for numeric comparisons like FIREFOX < 100 to be false in Chrome