Now, before you get all hot under the collar about the cookie issue, I suggest you visit, or revisit in the case you have already read Ben Edelman's analysis, sponsored by Clicks2Customers, in "Cookies Detected by Anti-Spyware Programs: The Current Status".
However, if you still want to make a change to Firefox, and we are talking about 3rd party cookies anyway, it can be easily made in Firefox about:config.
- Open a Firefox browser tab
- Type about:config in the address bar
- Scroll down the page to network.cookie.cookieBehavior
- If the value is 0 (zero), right click on that line and change the 0 to the number 1 (if it is already a 1, that means the configuration was carried over in the upgrade to 2.0).