For starters, they won't block tracking when you're using Facebook or Google itself. For PCs, Firefox also has an optional add-on, called Facebook Container, to segregate your Facebook activity from everything else. Facebook and Google declined comment on the Safari and Firefox tools. Google said its Chrome browser offers tools to control and delete cookies and set preferences for certain websites. Google says users can also decline personalization and get generic ads instead, though tracking continues in the background while using the company's services.