Why programming yourself. Web Standards are changing over the years, so maintenencing could be hard. I can recommend you Cliqz Browser
As far I know, this company is planning to monetize its browser soon by displaying "special offers" (or simply unwanted ads) to users. So I'd better stay with FF I was the OP, even if FF leaks some data.
Webcam and microphone spying are 100% legitimate concerns, and have been for years. I seriously don't understand why people would rather let their fear of something they don't understand force them into ignoring something so blatantly true. Can you, on your phone, record the phone calls? Can you, on your phone, take a picture? Is this same phone controlled by a series of software and applications that are connected, interact with, and are updated through the internet? Then other, determined and capable individuals, can do the same remotely.
We all know we are getting spyed on but programming your own browser... That's quite an ambitious project.
And even then you haven't stopped your ISP recording or any one of the hubs your requests bounce through
Using standard web technologies, including JavaScript, HTML and CSS, you can create a simple UWP application that contains inside WebView and implements basic functionality: navigation and work with your favorites. Such tricks can be used in any UWP-application for transparent integration of web content.
It should to a degree if the engine used is open source -- but then so would just using Chromium instead of Chrome. If you're REALLY worried about it, build from source. Chromium is the fully open source version of Chrome, where all development and testing takes place, as such it is open source with no spyware in it -- since if there were spyware the maintainers and anyone willing to look could find it, remove it, etc, etc. https://www.chromium.org/Home In that same way, nw.js and Electron are both built on Blink and V8, meaning if you care you could just dig through their code looking for spyware, which is why they have none. Webviews created in them are therefor reasonably safe. Though I wouldn't trust that for a UWP, given that's running Chakra (edge), f*** knows what spying for Microshaft that's doing. Hell I often wondered if that's why Microsoft themselves used Electron instead of their own web stack when they created Visual Studio Code. Even in-house they don't trust Edge or UWP. Also though, if you're REALLY paranoid, could always just run Tails on a VPN.
Unfortunately since he "no longer believes in using free Browsers like Firefox or Chrome as they are spying day & night" he has no way to keep us updated. Judging by his slick skills and uber intelligence I'm going to assume he is probably at least a months out from his first release. However, it's so anonymous we probably will never hear about it.
You can use https://sourceforge.net/projects/cyberfox/ which is open source and so you can view the source code and see if anything is wrong. I am also interested in this project. I have 14 years of programming experience. If you want to collaborate PM me.
Check the OP's post history here, even if this was a sales thread (which it isn't) he's not the sort of person you want to go into business with, he has a massive reputation for scamming people.