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Mozilla Says Intermediate CA Preloading Reduces Connection Errors in Firefox

Courtesy of the recently added Intermediate Certificate Authority (CA) Preloading feature, Firefox is handling secure connections better and users are experiencing fewer errors, Mozilla says.

The technique essentially consists of the browser pre-downloading all trusted Web Public Key Infrastructure (PKI) intermediate CA certificates through Mozilla’s Remote Settings infrastructure.

Thus, Firefox users won’t see an error page when the proper intermediate CA certificates are not specified, which, according to Mozilla, is one of the most commonly encountered issues when it comes to configuring TLS security.

For Intermediate CA Preloading, Mozilla enumerates all of the intermediate CA certificates in the trusted Web PKI, with the relevant ones available through the multi-browser Common CA Database (CCADB) reporting mechanisms.

“As a result of Mozilla’s leadership in the CA community, each CA in Mozilla’s Root Store Policy is required to disclose these intermediate CA certificates” to the CCADB, the browser maker explains.

Mozilla periodically synthesizes a list of intermediate CA certificates and then places the list into Remote Settings, with more than two thousand entries currently included in that list.

When first receiving the list, or when updates are made, Firefox downloads the necessary intermediate CA certificates in the background. With changes made to the list at a slow pace, keeping it updated is an easy task.

“Certificates provided via Intermediate CA Preloading are added to a local cache and are not imbued with trust. Trust is still derived from the standard Web PKI algorithms,” Mozilla explains.

According to the company, Intermediate CA Preloading in Firefox 68 has resulted in a lower number of unknown errors when a TLS handshake is performed.

“While there are other factors that affect the relative prevalence of this error, this data supports the conclusion that Intermediate CA Preloading is achieving the goal of avoiding these connection errors for Firefox users,” the company says.

While Intermediate CA Preloading is currently available for desktop users only, Mozilla plans on rolling it out for mobile users as well, to ensure they too encounter fewer secure connection errors.

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