After a brief delay, Mozilla finally distrusted all Symantec certificates with the release of Firefox 64 this week.

In October, Mozilla postponed the distrust deadline for Symantec certificates from Oct. 23 until the release of Firefox 64 this month. In 2017, Mozilla, Google and other major browser makers had agreed on a formal plan to remove trust for all Symantec certificates, including its GeoTrust, RapidSSL and Thawte brands.

The move came after Google engineers documented a "series of failures" within Symantec's public key infrastructure (PKI), including certificate misissuance, failures to remediate issues raised in audits and other bad habits that violated the Certificate Authority/Browser Forum's Baseline Requirements.

Symantec agreed to the browser makers' staged proposal to remove trust from its certificates by October of this year. Soon after the agreement was made, Symantec sold its PKI business to rival certificate authority DigiCert. While DigiCert has made progress moving customers off of the old Symantec certificates and onto new certificates issued through DigiCert's own PKI, Mozilla felt too many websites were still using certificates that would be on the verge of being distrusted. Google adhered to the original October deadline, but Mozilla gave DigiCert additional time to update customers' certificates.

Nevertheless, Dan Callahan, engineer with Mozilla Developer Relations, and Chris Mills, senior tech writer at Mozilla, had harsh words for the troubled Symantec PKI in the Firefox 64 release post.

"Due to a history of malpractice, Firefox 64 will not trust TLS certificates issued by Symantec (including under their GeoTrust, RapidSSL, and Thawte brands)," they wrote in the announcement. "Microsoft, Google, and Apple are implementing similar measures for their respective browsers."

It's unclear how many websites are still using distrusted Symantec certificates. Mozilla previously said "well over 1% of the top 1 million websites," according to Cisco Umbrella, were still using Symantec certificates as of October.

In addition to removing trust for Symantec certificates, Firefox 64 includes new features for enhanced tab management; a Task Manger page that shows how much energy each open tab is using; and Contextual Feature Recommender, which proactively recommends add-ons, extensions and features based on individual users' web activity.