Weird Discourse feature. New or new discovery?

Today for the first time in the years that I’ve been reading this site in Discourse on my phone, something new happened. While touching a thread subject in a forum, a preview box if the first post in the thread popped up. I was able to reproduce it by moving my finger from left to right across subjects instead of pressing the subject (a “swipe” instead of a “tap”) and it pops up and stays as long as I keep touching the screen.

Newly added, or something I somehow managed to not accidentally activate before?

What browser are you using when you get this?
I occasionally see the preview, but then Chrome’s context menu comes up.

I believe it is just the standard preview that works all the time on a computer with the mouse-over.

Firefox. Yes, it is the preview like you get with a mouse-over on XKCD but I’ve never had it happen on my phone before. (A long-press pops up an options menu.)

I haven’t used the site on a desktop computer since long before the switch over to Discourse, so while I knew it HAD mouse-over previews, I’ve never seen one before today.

And I see it doesn’t work on subjects from the main page, only from subforum pages.

I can tell you it isn’t a new feature.
Perhaps Firefox made a tweak where it now works better on Firefox on Phone.
It is basically useless in Chrome on a Phone. But that is Chrome causing the issue, not Discourse.

In our Admin Panel we have access to the “What’s New” from Discourse. Along with our Mod stuff and some built in reports.

That stopped working on windows laptop a while ago too.