> "Instead of forking Chromium or anything else, we're building our desktop app around the OS-provided rendering engines (like on mobile), allowing us to strip away a lot of the unnecessary cruft and clutter that's accumulated over the years in major browsers," explains Weinberg.
The same engine (WebKit) is available on all Apple platforms. One can also build a desktop browser on top of WebKit like DuckDuckGo suggests it may do on macOS. This approach has a tremendous advantage for solid platform integration and allows them to focus on building a good user experience (and, in this case, secure* good user experience).
It basically only lets them do a bit more than skinning it. No deep plugin architectures like you see with Android Firefox, allowing real ad blockers.
It is also possible to extend the content blocking feature, so it also works in Safari itself through a regular web plugin or a content blocker extension. DuckDuckGo offers the "DuckDuckGo Privacy Essentials" plugin for iOS and macOS, blocking all kinds of trackers.
How they will support Linux is a mystery.