new messenger opens links in EDGE instead of default browser.

This should open Messenger in your favorite browser...

Only if your favorite browser is Chrome. That doesn't work in Firefox for several reasons, and might not in other non-Chrome browsers either.

I believe Firefox has its own method of creating web apps, and it works fine in Vivaldi (Chromium-based). But a good app shouldn't NEED workarounds like this, is the point we're all still making to each other.

One might argue that a good web site doesn't need apps. Especially for services that are by nature online activities.

I think Firefox had this feature, but because the Mozilla team are super lame, they dropped it. But you can achieve it with a plugin. I think this one: https://addons.mozilla.org/en-US/firefox/addon/pwas-for-firefox/

I think there might be one called electron too.

In this web centric age, on an app centric OS, this feature is essential IMO. Even Microsoft is too lame to figure this out.

Installing using the link you provided worked. When Messenger prompted to update, I opted not to, now my links open in Chrome once again. Thanks!