> this looks like absolute hell, as someone who uses drag-n-drop between programs fairly often

The way people use it is you constantly reorder windows according to your workflow so DnD is not a problem.

> I'm also someone whose open browser tabs tend to grow indefinitely until I just have to bookmark and close all hundred of them or whatever

I agree the tab model is an horror. The problem is for most people the tabs are their browsing history, with a visual clutter.

My guess is there is an huge opportunity for rethinking the whole web browser history/tab model.

Another thing I hate especially in firefox is that one can't pin tabs on the right, next to the newest tabs and the new tabs button. So often one has to keep one or two tabs open but otherwise open many new ones to research something.

> I'm also someone whose open browser tabs tend to grow indefinitely until I just have to bookmark and close all hundred of them or whatever, so...

You might like the tabstash browser extension