Hey @NeuralBalance
Thank you so much for coming to the Klaviyo Community for help with your embedded signup form, happy to help!
I went to your website that you shared (which is beautifully done) and was able to see the signup form in Chrome and Firefox. Most likely it is one of the usual suspects that is preventing you from seeing it in your Firefox browser. Things to check: Firefox specific plugins, firewall, ad-blocker. Often with Firefox UBlock is a typical ad-blocker that prevents the signup form from displaying and just needs to be turned off or given permissions for your site. This is not a chronic issue as others have successfully used our embedded forms on Firefox. So definitely review all the items I mentioned before that would impact your browser as this will likely solve the issue. If this still does not resolve, please contact Klaviyo Support as they will be able to do a deep dive into your account for a solution.
Hope this helps, Thank you so much for being part of the Klaviyo Community!