The notes on browser privacy imo are too significant to have been relegated to a footnote:
As part of the drafting of the 2015 finding on Unsanctioned Web Tracking, the then-TAG (myself included) spent a great deal of time working through the details of potential fingerprinting vectors. What we came to realise was that only the Tor Browser had done the work to credibly analyise fingerprinting vectors and produce a coherent threat model. To the best of my knowledge, that remains true today.
Other vendors continue to publish gussied-up marketing documents and stroppy blog posts that purport to cover the same ground, but consistently fail to do so. It's truly objectionable that those same vendors also prevent users from chosing disciplined privacy-focused browsers.
To understand the difference, we can do a small thought experiment, enumerating what would be necessary to sand off currently-identifiable attributes of individual users. Because only 31 or 32 bits are needed to uniquely identify anybody (often less), we want a high safety factor. This means bundling users into very large crowds by removing distinct observable properties. To sand off variations between users, a truly private browser might:
- Run the entire browser in a VM in order to:
- Cap the number of CPU cores, frequency, and centralise on a single instruction set (e.g., emulating ARM when running on x86). Will likely result in a 2-5x slowdown.
- Ensure (high) fixed latency for all disk access.
- Set a uniform (low) cap on total memory.
- Disable hardware acceleration for all graphics and media.
- Disable JIT. Will slow JavaScript by 3-10x.
- Only allow a fixed set of fonts, screen sizes, pixel densities, gamuts, and refresh rates; no more resizing browsers with a mouse. The web will pixelated and drab and animations will feel choppy.
- Remove most accessibility settings.
- Remove the ability to install extensions.
- Eliminate direct typing and touch-based interactions, as those can leak timing information that's unique.
- Run all traffic through Tor or a similarly high-latency VPN egress nodes.
- Disable all reidentifying APIs (no more web-based video conferencing!)
Only the Tor project is shipping a browser anything like this today, and it's how you can tell that most of what passes for "privacy" features in other browsers are anti-annoyance and anti-creep-factor interventions; they matter, but won't end the digital panopticon.