For organizations interested in supporting Firefox on Windows in a managed environment, a longstanding hurdle has been that Firefox does not use the underlying platform’s certificate database when verifying TLS web server certificates. As an organization, having a separate transparent and open certificate authority program furthers Mozilla’s goal of fostering the open web. However, for users in managed environments attempting to connect to services that use non-public certificate hierarchies, this often results in a sub-optimal experience where Firefox will not connect while other browsers will.

To address this shortcoming, we have been developing an optional feature that, when enabled, will search the Windows certificate trust store for certificate authorities that have been added by the user or an administrator. If Firefox encounters any such CAs that are trusted to issue TLS web server certificates, it will incorporate those CAs into its own path building logic. When verifying a server certificate, if Firefox can find a path to one of those imported roots, the connection will succeed.

This feature is available in Firefox 49 and up (currently in beta). To give it a try, go to about:config and add the boolean preference security.enterprise_roots.enabled and set it to true. After that, Firefox should connect successfully to sites using certificates issued by 3rd party root certificates that have been added to the Windows trust database. Note that currently these root certificates will not appear in Firefox’s certificate manager as they are intended to be managed from the interfaces provided by Windows itself. This may change in the future.

But wait – there’s more! Using the same infrastructure, we have developed a similar feature to handle the case where Firefox is being used on an account that is being monitored by the Microsoft Family Safety functionality in Windows 8.1. For background information, this involves a local intercepting proxy that can log and/or block web traffic to and from an account. A similar feature existed briefly in Windows 10 but was reconfigured to only affect Edge. Starting with version 50, instead of showing the untrusted connection error page Firefox should “just work”.

These features are still in the early stages, so if you encounter any unexpected behavior, please feel free to file a bug.

This has been a guest post from David Keeler, Mozilla Engineer.