https://arstechnica.com/gadgets/2018/09/next-windows-10-update-triggers-outrage-by-continuing-to-promote-edge/

Every version of Windows 10 has included some amount of built-in promotion for Microsoft's Edge browser. The forthcoming major update, due to ship some time in October, includes a new screen, shown above, that will appear if you run the installers for Chrome or Firefox. The advertisement is on by default (though it can be disabled by following the "Open settings" link) and exists in addition to the smaller messages that appear when you actually run third-party browsers for the first time.

Most people will not see this message (if they're upgrading an existing Windows 10 machine and, hence, already have the non-Microsoft browser of their choosing installed) or may see it once (if they're installing a non-Microsoft browser on a fresh installation), and then, clicking "install anyway" does what you'd expect; the third-party browsers install, can be configured as the default browser, and run normally just as they always did.