Firefox Accounts encrypt user data with (a function of) a master key; that master key is encrypted with a key derived from the user's Firefox Account password.

Firefox Accounts encrypt user data with (a function of) a master key; that master key is encrypted with a key derived from the user's Firefox Account password. It would be completely insecure for Mozilla to know the user's password (because then they would be able to use the password to decrypt the master key & the master key to decrypt each private datum), so they have set up a protocol in which the user enters his password in his browser, and the browser performs some one-way operations on the password to authenticate. Sounds secure, right? The problem is that this happens in JavaScript which is downloaded from Mozilla's site. It would be trivial for Mozilla to target a single user with a piece of JavaScript which boils down to: if (username === 'target') { sendPlaintextPassword(); } The solution is for user login to be impossible through web pages, and only available via the browser UI. This would mean third parties would have the opportunity to audit the Firefox source code (e.g. Debian, Red Hat and other distros could check to see if the source they build is malicious). It would also mean that silently targetting a single user would be far less possible (they could still try to send that user a malicious browser if he automatically installs updates — but a security-conscious user gets his updates from a distro, not from Mozilla directly). It's a really nasty flaw, and the fact that they refuse to address it worries me: why don't they care about the security of their users? Why do they insist on maintaining a backdoor?