return function () {
  return this.parent
    .findDisplayedByCssSelector('my_css_selector')
    .moveMouseTo()
    .end();
};

firefox on windows_nt 10.0 - Suite Name - Test Name (1.548s)
UnknownCommand: [POST http:sessionUrl/moveto / {"element":"8acf9bee-180c-4bb0-8fe6-da1288be5abe"}] mouseMoveTo

"environments": [
  { "browserName": "chrome" },
  { "browserName": "firefox" }
],