My website (https://roekconsultancy.nl) is based on the Astrid v1.15 theme and uses the standard menu (Running WP v4.9.8). Unfortunately 1st & 2nd level submenus start flickering and behave strange in Firefox (v 63.0.1). This is especially the case with the “Services” menu item. In MS Edge all menu items work fine but there are some odd white (rendering) lines now and then. The latter is also the case with the Astrid demo site. Please help to resolve this.