I basically do this already with Firefox and TreeStyleTabs (but ad-hoc). Any middle mouse/ctrl+click I do on a link, opens in a new tab nested under the current one. So all HN stuff is under one tab that is collapsed, all GitHub stuff is under one and so one. Really effective when you do research, as you can do the initial search on Google, then every result you open goes under the existing tab, which is conveniently labeled via the <title> tag on the Google page.

https://www.businessinsider.com/how-to-organize-tabs-in-safa...