I want to see: (1) an open source privacy first web browser engine funded by the EU and (2) EU to mandate interoperability in "chat" and video conferencing applications.
I rather suspect that this would come with mandatory encryption backdoors.
Having worked on Firefox CI infrastructure years ago, it's a huge and complex setup. As I recall back then it was >100 compute hours per push.
Fork it and keep synching in from upstream, sure that's easy. But are you an independent browser?