This is similar to this previous question, but I believe it's a bit different^*.

Sites like GMail support a preference that pushes all traffic through the SSL edition of the site rather than the plain-text protocol.

For sites that don't offer such preferences (or ones that may, but I have been unable to find, like facebook), is there a way using only the browser (perhaps with a plugin or addon) to always try SSL first, and fall-back to plain-text iff SSL fails?

Is that solution available on Windows, Mac OS X, and Linux? Just one?

^{_{* The previous question was looking for external applications that would accomplish this goal.}}