The idea here is to make it a bit easier to see how well the various players in the fediverse support the C2S side of the ActivityPub spec.
You can punch in any ActivityPub discoverable web url or fediverse handle, and BrowserPub will discover and display the underlying AP:
e.g.
social profiles: https://browser.pub/https://mastodon.social/@mastodon
or posts:
https://browser.pub/https://mastodon.social/@Gargron/113005517546136592
or fediverse handles:
https://browser.pub/@Gargron@mastodon.social
or even usernames (defaults to mastodon.social for now):
https://browser.pub/Gargron