An upcoming version of Firefox will block cross site tracking by default.
From an official Firefox blog post:
In the physical world, users wouldn’t expect hundreds of vendors to follow them from store to store, spying on the products they look at or purchase. Users have the same expectations of privacy on the web, and yet in reality, they are tracked wherever they go. Most web browsers fail to help users get the level of privacy they expect and deserve. In order to help give users the private web browsing experience they expect and deserve, Firefox will strip cookies and block storage access from third-party tracking content.
The post also says Firefox 65 will also fight browser fingerprinting, which is one of the many ways websites track you online.
You could argue that Firefox is late to the party here: Apple’s Safari already offers a similar feature called Intelligent Tracking Prevention, and an upcoming version of Safari will fight browser fingerprinting. But it’s good to see a cross-platform browser implement these features, because it’s unlikely that Google Chrome is going to do anything that potentially hurts ad revenue any time soon.