story
The idea behind TLS is that the client and the server agree on a temporary key to exchange the information in a secure way (there's a ton of literature on it) without saving the key locally. The good news is that it is something already implemented in a safe way in all sufficiently recent browser (for sufficiently recent I mean, sufficiently recent to support plugins, because also IE 6 supports some old form of SSL) and make them available to plugins.
TL;DR: It's trivial to do it right, screwing it up in this way means they have no clue on what security means.