Hey, just went on your site with firefox and the content was outside the screen. After digging into it a bit I found that you use "transform: scale(1.3)" on the body. It seems like firefox is positioning the element with its original dimensions and then scales the element. "transform-origin: 0 0" fixed it for me.
Thanks a ton for letting me know about it and sharing the fix as well. Fixed it now. Will spend sometime soon and sort the other Firefox issues that I discovered as well.
