I'd like to point you to this firefox extension HTTPS Everywhere (June 17th, 2010) and SSLGuard which is also a firefox extension (first released Oct 14th, 2009).
The code of the former extension is a lot more complicated and the result is not always quite the same as SSLGuard. In fact, while they support secure cookies and per-website custom rules, SSLGuard lets you add custom websites to be secured directly from a friendly graphical dialog.
You could even install both of them, apparently they don't conflict.
It's the second time decrew ideas are being duplicated. This happened sometimes ago with SSLtoHTML (ettercap plugin) and sslstrip (standalone application), but they released the code before us. Funny isn't it?
I'm not complaining about anything (I'm not saying "copy", I say "duplicate"), just clearing things out. Of course, better have more choice and more works.