Pretty sure the user is wrong about what caused this dialog. It was the recent Firefox update.
Firefox 80 added being a PDF reader as a Windows-selectable preference, as seen in this dialog. Whenever a new app for a given filetype is added, Windows asks you which one you want to use.
While Edge getting a special category at the top is annoying, this showcases the uphill battle Microsoft faces, where they get blamed for the actions of other software and user stupidity on a regular basis, because people don't understand how Windows works, in general.
Firefox 80 added being a PDF reader as a Windows-selectable preference, as seen in this dialog. Whenever a new app for a given filetype is added, Windows asks you which one you want to use.
While Edge getting a special category at the top is annoying, this showcases the uphill battle Microsoft faces, where they get blamed for the actions of other software and user stupidity on a regular basis, because people don't understand how Windows works, in general.