You could break on [EnsureWinWebAuthnModuleLoaded](https://searchfox.org/mozilla-central/rev/b4860b54810539f0e4ab1fc46a3246daf2428439/dom/webauthn/WinWebAuthnService.cpp#65) (parent process) and see where it fails. I know some VMs intercept webauthn.dll so that they can redirect WebAuthn requests to the host, so it's possible that you aren't using the standard Windows webauthn.dll.pass-through
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You could break on [EnsureWinWebAuthnModuleLoaded](https://searchfox.org/mozilla-central/rev/b4860b54810539f0e4ab1fc46a3246daf2428439/dom/webauthn/WinWebAuthnService.cpp#65) (parent process) and see where it fails. I know some VMs intercept webauthn.dll so that they can redirect WebAuthn requests to the host, so it's possible that you aren't using the standard Windows webauthn.dll.