Save/Read user data across different browsers

I have been trying to figure this out for a couple of days now. My machine is a Mac with Snow Leopard installed.

I listen to music on http://listen.grooveshark.com/ using firefox, and I do not have a user account with them. When I leave the site and come back using firefox, I get an option to restore the songs that I had added to my playlist.

I figured that this feature was us开发者_开发百科ing simple cookies and there was nothing special to it, but the other day firefox was running slow [big surprise!] so I decided to use chrome instead. I was very surprised when I got the option to restore my playlist on chrome even though I've never accessed the site with it before. I was even more surprised when it restored the same playlist I had created using firefox, this blew my mind because I know that cookies are only supposed to readable by the browser and site that created them. I tried the site on Safari and I the same thing happened there too.

Are there any programming tricks/methods you know of that will make something like this possible? I ruled out the possibility that the site is using my ip-address to remember me because other people on my internal network [we share the same public ip address] use grooveshark too and we all have separate playlists.

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Adobe Flash player is a cross-browser technology that allows this.