[0] has some more information – it appears to be standard OpenPGP with a random encryption key stored on the server of safegmail and then retrieved by the receiver, using a common secret as identification. Given that you have to install a (closed-source?) extension and that the key management happens on the servers of safegmail, you naturally have to trust them not to do funny things with your data.
Years ago, there was a Firefox extension to do standard GnuPG in the browser, but I think it died down. If you want really secure email at the moment, I assume there to be no other way than to use a client with PGP support, such as, uh, basically every email client.
Years ago, there was a Firefox extension to do standard GnuPG in the browser, but I think it died down. If you want really secure email at the moment, I assume there to be no other way than to use a client with PGP support, such as, uh, basically every email client.
[0] http://safegmail.com/information.html