A 307 is most likely an HSTS redirect that has almost nothing to do with Cloudflare. Those other domains probably have full **HSTS enabled in SSL/TLS -> Edge Certificates (include Subdomains).**
This gets you a response header like this: strict-transport-security: max-age=31536000; includeSubDomains; preload
And a site that’s listed at hstspreload.org will trigger a 307 redirect in Firefox immediately. Sites with just the header will trigger a reload after first visit because Firefox will remember that HSTS header.
I checked your domain, and it doesn’t have that header.