For anyone who comes straight to the comments, I recommend passing on this article. If you already clicked through, I'm sorry :)
It it misleading, the writer is only considering desktop usage, and then constraining the data the the month of March. The 'evidence' is in the form of a single screenshot, from his lone data source NetMarketShare. He is trying to hype it up as some sort of 'grand' milestone.
Here is another data source that says otherwise - https://gs.statcounter.com/browser-market-share/desktop/worl.... Other commenters have also pointed out data that conflicts this premise.
It is poorly written, and over the top. The poster used the subtitle here, but the real title of the article is 'History in the Making: Microsoft Edge Overtakes Mozilla Firefox'. Also making points such as "While some expect Microsoft Edge to become the world’s top desktop browser...". Come on man.
Finally, it is just not that interesting. The real story should be, some Firefox/ IE users decided to try out the new Edge in the month of March, after a flashy new version was released. Maybe Edge really will continue to claw a few points of market share, let's follow up in a few months. But this particular article is really poor.