Your security certificate expired today, June 16, 2019. Firefox will not allow me to connect unless I accept the invalid cert. Most casual users will not do this. Your cert needs to be renewed ASAP.
No problems here. Likely you're not getting Cert updates or you need to clear your cache. Roku for me shows it's valid until 2020. Make sure you don't block Windows Updates completely, that's how MS keeps your Certs updated (even for other Browsers).