This move by Microsoft may probably help Microsoft have Windows users using its browser, but I seriously doubt if it's good for the web.
There are people claiming that Microsoft could easily fork from Chromium, but honestly, do you see that happening in the next few years? Having read that Microsoft's Edge team was a very small one, I don't believe Microsoft will fork Chromium anytime in the next two or three years (no financial incentive, which could be a big motive, to do so)...and that's a long time to keep pushing the Chrome/Chromium way ("what Google wants for the web").
As an aside, I very much liked this article linked within, titled "The ecological impact of browser diversity" by Rachel Nabors. [1]
To all those who evangelize Firefox, please also see if you can donate money to Mozilla. It may seem like Mozilla has a lot of money (more than 90% coming from Google for being the default search engine added in the browser), but this is not enough, and could turn to be nothing if Firefox's market share becomes next to nothing and Google decides to pull the plug when the current contract expires. Partnerships with Bing (or other search engines that not many people use) may not bring in as much money to Mozilla.
Read about all the work that Mozilla does (aka "not just Firefox") in its "State of Mozilla 2017" annual report. [2] The audited financial report is here. [3]
[1]: https://css-tricks.com/the-ecological-impact-of-browser-dive...
[2]: https://www.mozilla.org/en-US/foundation/annualreport/2017/
[3]: https://assets.mozilla.net/annualreport/2017/mozilla-fdn-201...