This is a known issue for the NX product line and we do have a small update that can be applied to resolve this behavior, available at the link below.
Please note that this does require a restart of the system, so it will require a small window of downtime.
If you cannot schedule downtime immediately, the following workaround can be used to bypass the security warning in newer versions of Firefox, to alleviate the issue until downtime can be scheduled.
- Enter "about:config" into the firefox address bar (confirm the info message in case it shows up)
- Search for bold preferences starting with security (most likely these will be "security.ssl.errorReporting.automatic" and "security.tls.version.min")
- Right-click and reset those entries to their default values