SAN FRANCISCO: Google is reportedly developing a tracker that would replace third-party cookies, while rival tech firm Mozilla continues to test a third-party cookie patch of its own.

Advertisers and ad networks using the Google system would have access to the "anonymous identifier for advertising", known as the AdID, as long as they agreed to basic guidelines.

Both companies' products would potentially give consumers greater control over their online privacy.

Not everyone in the advertising industry was convinced this was a positive move. "Restricting third-party cookies isn't going to make relevant advertising go away; it just hands more power to big companies," Zach Coelius, CEO of ad technology firm Triggit, told USA Today.

Meanwhile the Interactive Advertising Bureau, which represents the industry, said was concerned about the implications of leaving such ad identifiers in the hands of a few large companies.

"They could deprecate the use of that ID on a whim, basically, and severely undermine billions of dollars in digital ad spending," said Mike Zaneis, IAB general counsel.

IAB president Randall Rothenberg has also been highly critical of Mozilla's decision to block third party cookies by default on its Firefox browser but that has yet to be implemented as the company indicated it was still testing the relevant patch.

Mozilla's chief technology officer Brendan Eich told Ad Exchanger it "had two edges to it". He explained that the patch blocked cookies that were valuable to the user and sometimes allowed cookies that should not have been set.

Another issue was that it presumed first party cookies, which are owned by online publishers, were good and third-party cookies bad, which was not necessarily Mozilla's position.

Denelle Dixon-Thayer, Mozilla's general counsel, denied that the company struggled to reconcile its role as an advocate for consumer privacy with its sale of advertising. She argued that it was about bringing personalised content, whether advertising or other material, to the user and having the user understand the value exchange.

"I think if most users understood that in order for them to get this content for free, they may be giving up a little bit of their information, they may choose to do that or choose to pay," she said.

"The conflict is just in the fact that users may not have that information, and so may not be able to make that decision."

Data sourced from USA Today, Ad Exchanger; additional content by Warc staff