Dan Friedman has further clarified Google's stance on endorsing or bringing attention to the Pay Per Click referrals (such as Firefox and Adwords).
"If you encourage people to download and install Pack on your site and the conversion rate goes up, we're happy to pay the additional cost, because it directly translates to more Pack users for us.Dan had told all this to me the last time I spoke with him on the phone - I even posted about it at DP Forums but I'm sure nobody was going to take my word for it. Now that it is official many publishers should be able to significantly increase their earnings with Google's referral products.
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Any endorsement or attention drawn to a referral ad must be done in a way that supports the intended use of the product or service associated with it.In short, our policies on endorsing ads are based on our concern for the visitor, the advertiser, and the publisher."