I've been using Gingko Writer [1] since it was "gingkoapp" -- it's similar in how information is structured (hierarchical vs linear), but focused on creating, not consuming. The tool permits a rather free-flow approach to compiling things in various scopes [2], and can render a final linear work product from it.

OP's browser and gingko mashed up together would be the perfect thing -- find/explore/learn, annotate, synthesize, organize, and combine into a finished thing, be it a reference or a proof.

1: https://gingkowriter.com/

2: https://vimeo.com/639232763