This document discusses changes in Firefox and Safari that block third-party cookies by default. It notes that first-party cookies and JavaScript will still work for third-parties if they already have cookies set as first-party. However, this change makes it difficult for companies to reliably track audience overlap between separate domains. It also negatively impacts data brokers and small publishers who rely on data-enhanced ad revenue. Possible solutions discussed include HTML5 local storage and workarounds like browser fingerprinting.

2. FIRST-PARTY THIRD-PARTY
 foo.com  doubleclick.net
 bar.foo.com  webtrendslive.com
 foo.bar.foo.com  foo.112.2o7.net

3. JavaScript HTTP header
response
 
First-party
 
Third-party

4.  New Firefox default is to block third-party
cookies
 Safari has done this for a while
 Detail:
 Blocks setting cookies from third-party domains
that have no existing cookies set as first-party
 i.e., Facebook will still be able to track you

7.  Reliably(*) track the shared audience
between separate domains
foo.com
bar.com ooo.com
* Except Safari

8.  Google Analytics uses first-party cookies
exclusively
 Passes cookie ID between domains only
when users click from one to the other
 Can’t reliably measure audience overlap

9.  Web analytics vendors need to find a solution
 Data brokers are screwed
 Small publishers will lose data-enhanced ad
revenue

10.  Moving to HTML5 localStorage late this week
 Interesting side effect:
 localStorage is isolated by scheme + hostname +
port (HTML5 Origin)
 Not really a problem though
 See: http://htmlui.com/blog/2011-08-23-5-
obscure-facts-about-html5-localstorage.html

11. If the domain already has cookies, it
can set them third-party
 Facebook will be fine
 Google will be fine
 Fairfax, News will problably be fine
 Web analytics can probably find a workable
solution

16.  Iframe hack: Google got caught using this
 Browser fingerprinting
 Bounce users through your domains? iJento
do this
 HTML5 localStorage

17.  From iPhone or Firefox Nightly:
 http://arseh.at/cookie

18.  Vendors:
 David Jordine @Adobe
 Mark Allison @WebTrends
 Sauli Happonen @Nielsen
 Chaoming Li
 NarbehYousefian