Live Preview failing in Safari and Firefox only
CORS (or Cross-Origin Resource Sharing) issues usually occur when you are attempting to load a resource such as a font, a stylesheet, or a script from a remote location that does not give your domain explicit permission to access it. Thinking the resource is unsafe, your browser will block it.  

Are these pages attempting to load any resources from remote locations such as a CDN or web storage like an S3 bucket? If so, you may need to edit your CORS policy for those services to mark your resources as "safe" for your domain.