I think firefox has everything you need already. I use librewolf in linux but any firefox on a desktop OS should behave in the way I describe below.
> i want rich bookmark behavior.
This points needs specifics. What do we mean by rich? what are the outcomes we're trying to achieve?
> i want to be able to quickly load common favorite news sites & blogs.
> or load a window with all my productivity SaaS sites.
This can be easily achieved through folders in a bookmarks toolbar. For example I have a folder called 'News' with my top 4 sites. When I open the browser, I just right-click on the 'News' folder, click on "open all bookmarks" and those sites open on a tab each.
One click and half a second... very efficient!
> or pick up where i left off on a research rabbit hole.
> and i want it to be intuitive, efficient, and a prominent UX feature set.
In a rabbit hole window with X tabs -> right click on the tabs area -> select all tabs -> bookmark tabs -> then from there you can create folder 'rh 17 August'
Next time you open a browser, just right click on that folder and open all. When done, just delete the folder.
Once you learn this, it's a one or two second process so it's very efficient in my view.
You might argue that this option could become a one-click thing (ie a right-click menu item called 'save all tabs as bookmarks' and use an automated name) but that brings a whole new range of problems (cluttered interface for users that don't want this, and therefore decrease in overall UI efficiency)
> i'm not alone right?
No, many people like me relies on bookmarks. I share the frustration others shared around the bookmarks toolbar being hidden by default. However, by using standard behaviour I manage to make bookmarks work in a pretty efficient way.