Thanks for reaching out. I use firefox regularly with FusionAuth and haven't seen this behavior. As I'm sure you know, troubleshooting these kinds of issues is really tough without precise steps to replicate the issue. I am glad that you can use chrome, however.
2020-11-02T09:12:47.670831893Z 2020-11-02 9:12:47.670 AM ERROR io.fusionauth.app.primeframework.error.ExceptionExceptionHandler - An unhandled exception was thrown
2020-11-02T09:12:47.670862293Z java.lang.NullPointerException: null
2020-11-02T09:12:47.670866593Z at io.fusionauth.api.service.authentication.SAMLv2IdentityProviderAuthenticationService.start(SAMLv2IdentityProviderAuthenticationService.java:176)
2020-11-02T09:12:47.670870593Z at io.fusionauth.app.action.api.identityProvider.StartAction.post(StartAction.java:61)
I looked through our github issues and didn't see any open or closed issues about this functionality. So I think our current stance is, as the SO answer says:
There are many potential types of limits that could be put in place, such as limiting by IP, device, geographic location, session count, etc that these types of limits may be best solved by a Web Application Firewall (WAF) or some other specialized network security product.
However, we love to hear from users how to improve FusionAuth.
If this is an important issue to you, per our roadmap guidance, if you are a community member, please file a github issue. If you have an edition with support, please open a support ticket.
Thanks for using FusionAuth. Sorry about the confusion.
There are three ways to do FusionAuth registration:
using the APIs and building your own UX
using the basic self service registration with hosted login pages <-- this sounds like what you are looking for
using advanced self service registration with hosted login pages (only available with a paid license -- pricing starts at $125/month for this and other premium features)