If the referrer header contains the full URL from which the user came from it could contain something the user deems private. Imagine that the URL contains a s

If the referrer header contains the full URL from which the user came from it could contain something the user deems private. Imagine that the URL contains a search string that contains something the user might deem private, or the article is about something a state may deem to be illegal, etc. This may not be PII but it could be deemed private by the user. The user should be in control of what information could be given to a website. Imagine a scenario where a person is a member of a group that is looking for equal rights in a country that is very much opposed to this. The group uses a tool that happens to make it clear who this group is. The group then links to an article about their cause or similar. Now that country could potentially link things together and demand information about everyone in that group. It's amazing how little bits of information about you can get you in hot water. This is a good move imo, and I'm glad that Mozilla is trying to plug these types of things. It's better for everyone. As an aside, moving to a privacy oriented browser could very well get Firefox more users. Just like Apple's play to being a private and secure mobile OS is getting them users.