Your comment could just as well have said SGML or XML instead of JSON which would make the distinction more obvious.
If you send an HTTP request with an header of 'Accept: application/activity+json' you get proper machine-readable data out.
Given the context I assumed the regular unspecified internal type of JSON commonly used to back SPAs
[1] https://addons.mozilla.org/en-US/firefox/addon/rsspreview/
Both are vastly inferior and tedious ways requiring me to type a new URL. It is not controverserial to say the primary purpose of a web browser is to display HTML. Most URLs resolve to HTML pages. It's been this way for 30 years. Only in the last 10 has this radical new application view of the web been creating walled gardens on top of the old document model web. And that's mostly for commercial/profit-motive reasons so it's sad to see non-profit motive software cargo culting SPA only dev.
It also means post v3 mastadon is inherently incompatible with indieweb standards like webmention since there is no page to check for URLs.
IIRC, (some) browsers used to have a feature that allowed you to browse a web page that had XML content, such as http://a.com/b.xml .
You could expand and collapse nodes. Or maybe I remember it as being for XML, but it was actually for RSS. After all, RSS is an XML format or application - is that the right term?
See the Example section at:
https://en.m.wikipedia.org/wiki/RSS
Haven't checked lately if browsers still do.
For reference, here's the JSON endpoint for the same account as listed in the article: https://mastodon.online/api/v1/accounts/109298336948075673/s...
Firefox has a nice UI for browsing JSON, but Chrome will just give you a text dump. Ironically, Firefox also used to have a nice UI for browsing RSS feeds but they removed it awhile ago.