It's not just Firefox that is having this issue. I've also seen Mac users posting they are also seeing the issue in Safari. I have tried all updated versions of Chrome, Edge and Firefox and all get this error.

If you go to any other page on Walmart's site, like walmart.com/tv, it works and then you can click on the home page icon which brings you successfully to walmart.com. If you go directly to walmart.com without going to another page on Walmart's site, it always fails.