Indeed. If you add an unsigned plugin (that is, one lacking a .safariextz file) to Extension Builder and try to install it from there, and you do not already ha

Indeed. If you add an unsigned plugin (that is, one lacking a .safariextz file) to Extension Builder and try to install it from there, and you do not already have a developer certificate, you will see the message, "Without a Safari Extensions Certificate, this extension will only be available until you quit Safari." And it will be so.