Oh, by "js contexts" do they mean "all the javascripts related to the page?" If so, then I guess this file tree-like explorer of js is the Firefox equivalent?
No, each context can contain multiple scripts. Each browser tab has a single top-level context called 'top', plus it will have extra contexts for any frames or iframes within the page, as well as for any browser extensions running on the page.
Only script elements in the HTML of the top-level page (i.e. in the HTML served directly from the URL you see in the location bar) get to be in the 'top' context.
https://imgur.com/a/YvA9Hdw