I look forward to MS's new browser being as resource hungry as chrome.
I don't know what to do if Firefox starts to really shit the bed.
Speculation points to performance being the reason Microsoft is doing this. Put this way:
All OS makers these days provide a "core browser" view for app makers to use. On iOS this is WKWebView based on Safari, on Windows it's EdgeHTML based on Edge. These "built-in" browsers are much more performant than third-party ones because of their integration with the host OS.
However, on Windows, app makers aren't limited in their choice of engine like they are on iOS. This means they go with what's popular, and what's popular is Chrome/Chromium. Chromium forms the heart of a cross-OS app container called Electron, which basically packages a web app into an EXE. Slack, WhatsApps' desktop client, and even Microsoft's new version of Skype use it.
These apps would otherwise never have been as performant on Windows as if they had used EdgeHTML, but EdgeHTML is
so far, far behind Chromium on features as a "drop-in app platform" that Microsoft has decided to give up, and make Chromium the new Windows browser engine instead.
What this means is that everyone wins and we get the best of bost worlds. Microsoft still "gets their own browser" (for marketing purposes), but performance on Electron and Chromium-based apps/browsers will improve significantly once it becomes as integrated into Windows as Edge currently is.
The only people who are (rightfully) mourning this are web developers, who are fearful of another web monoculture developing and potentially impeding future progress. But those concerns, even if valid, are on a much longer timeline in the future.