Im more interested in how FixProxy works, is it basically a filter that disallows tracking and javascript? with optional whitelists for sites you trust. I think this would be more useful for users who like to take privacy and control into their own hands. There is basically no reason to write your own browser if you approach the problem like this. I suppose this is what ublock is to a degree.
Yeah it processes the HTML+CSS, applies the fix scripts so web pages that wouldn't work without JS are fixed to be usable. Then it applies whitelist to all HTML elements/attributes and CSS rules. This is then converted back to HTML+CSS for the web browser to show.
It is very useful, I've been using it myself for multiple years with good results.
Having own browser is to reduce the memory requirements further. Even with FixProxy the normal browsers use a lot of memory, sure it's better than normally but still a lot.
With FixBrowser the memory requirements are much lesser and it's much more portable, for example to older systems or computers with weak specifications.
