Mozilla says it regretted staying silent when it found out last week that hackers had stolen digital certificates. The certificates were for six Web sites, including Google, Skype, Microsoft, Yahoo and Mozilla’s own add-on site. Hackers used a valid username and password to obtain nine SSL certificates from an Comodo certificate reseller. Comodo disclosed the breach of its reseller and theft of the certificates on March 23. A researcher at the University of Washington’s Security and Privacy Research Lab had urged Mozilla to warn users rather than ship a blacklist update.”]