Microsoft's new feature is expected in the release candidate version of Internet Explorer 9 that's due early next year. To put the feature to work, users will turn it on and select a list of sites to block.

Of course, like so many software features, how well it works depends largely on how well users understand it and make it work for them. As my PCWorld colleague Tony Bradley recently pointed out, could play a significant role.

Problems could exist, in other words, between the keyboard and the chair (PEBKAC).

Opting Out by Default

Over at Mozilla, meanwhile, have actually been going on since May of this year about the possibility of allowing third-party cookies only until a Firefox session is closed. Effectively, that would mean that the user opts out of online tracking by default.