https://www.bleepingcomputer.com/news/microsoft/microsoft-re...
Microsoft's other software uses "microsoft-edge://" links which simply ignore the user's default browser choice and open in Edge. When a workaround was found to fix this (i.e. to obey the user's choice), Microsoft blocked it.
Plus Microsoft rushed out this Edge-link workaround patch to retail, while sitting on the default browser UI improvements until next year.
1. This article is about Windows and Microsoft applications forcing use of Edge, ignoring your default browser entirely.
2. Your article is about setting your default browser.
The issue at hand though has to do with other links within windows that open web pages. Microsoft had used a different protocol (not https, but, something like microsoft-edge://). I think these links are like news items that show up in the start menu, etc. There was no way to set Firefox to open these links with what Windows provided, it only opened in Edge. A program was written that listens for these protocols, and would let the user customize what program opened with those links were clicked. Microsoft has now shut that option down.