As the headers go, here's my current thoughts on each:
- Content-Security-Policy: we're considering it, Report-Only is live on superuser.com today.
- Public-Key-Pins: we are very unlikely to deploy this. Whenever we have to change our certificates it makes life extremely dangerous for little benefit.
- X-XSS-Protection: considering it, but a lot of cross-network many-domain considerations here that most other people don't have or have as many of.
- X-Content-Type-Options: we'll likely deploy this later, there was a quirk with SVG which has passed now.
- Referrer-Policy: probably will not deploy this. We're an open book.