According to this post the Ad-ID is not accessible in the browser:
http://blog.adfonic.com/advertisers-2/ios-6-for-mobile-advertising-part-one-smarter-identification-through-ifa/
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Device identification on Apple devices – which are a hugely important
part of the mobile advertising ecosystem – is still not entirely
resolved. IFA is still available only in-app, not in the browser, so
the conversion tracking wars will continue.
Until the transition has completely happened, conversion tracking will
be less elegant and effective than it could be. While this isn’t a
huge problem, we would like to see this issue resolved once and for
all. People got scared over the UDID security breach, so the less
complexity around identification, the better.
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