The Winders 10 upgrade sets Microsoft's new Edge browser as the default , which has Mozilla raising a ruckus. Edge is designed to be sleeker and faster, similar to #2 - ranked Chrome (Mozilla's Firefox browser runs in at third place, well below IE and Chrome). Of course, you can restore the browser of your choice to be the default, but it takes a few steps:
The Windows 10 upgrade doesn't uninstall rival browsers from users' machines, but if users choose to restore Chrome or Firefox as their default browsers, they must launch their browser of choice and go through a couple of steps to instruct Windows 10 of their preference. Illustrating the process, Mozilla created a tutorial to help Firefox user upgrading to Windows 10 restore their browser preferences.
The MSFT decision regarding Edge is unsurprising; Winders 10 is an integrated package that's supposed to deliver a seamless experience, which they could never ensure if they didn't make their product default to a product specifically designed to play well with their OS. That they included a way to make another product the default is actually a plus, rather than a minus.