I have an Illustrator document with A4 size and export it as PNG with 300 ppi for printing (you can see it here in case it helps). On Safari and Firefox, printing that image from the browser with A4 paper results in 2 pages (whereas downloading it and printing from the operating system scales it to fit one page). I can print it on one page by scaling it down to 93% on the browser; when I scale the design down to 93%, I get the same problem. I also decreased the artboard size by 3mm on each side and tried a much smaller version with the same ratio (1.44, square root of 2), both giving the same problem.
What is a safe artboard size when printing directly from modern browsers?