I wonder if a extension to deal with flash cookies can be created. As far as I tested, the incognito mode doesn't take care of flash cookies. For people who don't know, flash cookies are pieces of info stored by Flash plugin in folders on our computers, outlasting indefinitetly. Usually are stored in :

C:\Users\UserName\AppData\Roaming\Macromedia\Flash Player

I think it would be enough for the extension to delete flash cookies on browser exit.

Try using CCleaner, it takes care of a lot of other things too.

CCleaner is a freeware system optimization, privacy and cleaning tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. Additionally it contains a fully featured registry cleaner. But the best part is that it's fast (normally taking less than a second to run)

Yes, that is what I do now. But sometimes can forget to run it... In Firefox there is an extension called BetterPrivacy who takes care of this things.

You can configure CCleaner to do its thing automatically at shutdown or at boot-up time...

Plus it takes cares of a lot more things also...