Cross Browser Css Parallax Issue

Hi WPMUDEV Support,

We are trying build a css parallax page in our website base on this link.
http://keithclark.co.uk/articles/pure-css-parallax-websites/

However, seems like only Chrome are able to work. Other browsers like Firefox, Safari are not working like Chrome does. Maybe css perspective issue?

The page link is demo-lemonade.com/lemonade/.

Kindly assist on the issue.

Thank you in advance.

Warmest Regards,
Terence