Tracking cookies

Has there ever been a FF addon that instead of denying or blocking, instead just scrambles tracking cookies?

Hm. My guess is that you would like to avoid being tracked while not being denied access to resources that depend on accepting cookies (otherwise, why not just refuse to accept them.) The problem is, under most circumstances, scrambling a cookie would have the same effect as not having accepted it in the first place -- the application will still complain about some data that it stored that it wasn't able to retrieve.

This is because, nowadays, most web apps aren't storing raw data in the cookies, they're just using them as unique identifiers to lookup the data on the server side. Scramble the unique identifier, and most apps will just say "I don't know what to do with this" and complain about you not accepting cookies.

The only exception would be if it were to scramble the cookie value to exactly match someone else's, in which case you'd effectively be hijacking their session. The chances of this are very, very small, though.

Really, what you want to do is not disallow cookies globally, but be selective about which ones you accept. There are extension (CookieSafe comes to mind) that let you block specific cookies on specific sites. Then you can accept the cookies that you absolutely need to conduct your business and reject the ones that are there for advertising purposes, etc. (The real devious sites will insist that you be tracked anyway, and the solution there is to do business with someone else.)

Just "accept for session only" on cookies by default.
That way they get wiped whenever you exit from Firefox.

Cheers