Personal web history referral graph with clustering

When doing research or just navigating I find myself opening multiple tabs that I wan't to deep dive in later but never have the time to. This leads to leaving multiple tabs open in my browser which I eventually group in different windows but still leave untouched. After some days/weeks I sometimes save each "Research Session" window in a Session using FFs Tab Session Manager extension. However, the flow of that research session is lost.

Is there any extension or tool with which one can visualize the web history as a graph, seeing which site lead to which and maybe clustering nodes by topic?

How do you personally keep track of such sessions? I am too lazy to transfer the knowledge from those sites to some knowledge base or to use bookmarks with categories (I like the idea of being aware of the referral that brought me to a particular site).