For one, the Instagram post says "Full story in my highlights (THE MIRROR)" but I can't figure out how to actually view those highlights. (Without creating an account at least.)

Can't, those are login-walled.

We post WSJ and NYT all the time though and it’s explicitly allowed last I complained about it.

There exist a few shady scrapers out there [0] which ahem mirror Instagram content. (Be sure to use an ad blocker if you try them, I can't vouch for anything beyond the fact that it does work)

[0] https://imginn.com/stories/wheatpraylove/

Off topic, but does anyone know why when I click on the above link in Firefox the back history is gone as if it was opened in a fresh tab? IG doing sketchy stuff to discourage navigating back to where I came from? Or perhaps the Firefox Facebook container protecting me?

It opens Facebook and Instagram in a Facebook container by default. The container has no history.

Ugh, that seems like a bug which should be fixed. It's pretty inconvenient for users. :(

Probably not trivial since the back button might be linked to history and the container is doing it's job in isolation.

I would expect there is a setting to force opening the container in a new tab if you want to be able to go back.

I think a new tab for the container and leaving the original tab open would be the least surprising/inconvenient behaviour.

There must be since that's how it works for me. Either I changed it, or it stopped being default at some point.

You can change that in the settings. It's under 'Tabs' in the 'General' section of 'Settings' from the hamburger menu in the top-right (check/uncheck "Enable Container Tabs").

I quite like having that on by default.

The extra security aspect seems important, but the browser shouldn't just drop the user's previous history (for that tab) just because it's isolating things. :/

Hopefully this is just a case of "early stage feature" and bugs like this will be fixed. :)