The following is a known issue with WebTitan OTG 2 for Mac.

Issue

Firefox returns a certificate warning instead of a WebTitan block page.

Cause

Firefox uses an internal certificate store and by default, it ignores certificates stored in OS.

Workaround (A)

Import a trusted certificate into Firefox manually. See Importing SSL Certificate in Mozilla Firefox.

Workaround (B)

If a trusted certificate has already been imported into keychain, follow the steps below to tell Firefox to trust this certificate:

  1. Open Firefox.

  2. Enter about:config in the address bar and continue to the list of preferences.

  3. Set the preference security.enterprise_roots.enabled to true.

  4. Restart Firefox.

See https://support.mozilla.org/en-US/kb/setting-certificate-authorities-firefox