BTW: Mozilla was not completely correct.
If you choose Express Settings during the upgrade, Edge becomes your default browser. If you revert to Microsoft's recommendations...Edge becomes the default. (That should surprise no one.) But if you choose the Customize options...which I always have...you can turn off the default browser selection, and use whatever your current browser is.
Another thought. The default browser selector shows ALL your installed browsers. So you can turn off the "make this your default browser?" permanently in all of them where it's needed...and just do it here. That makes more sense, and will work better for us once we get used to it.
Nice to know this. Even though I could figure it out, I, for one, do not like having something foisted on me. I've not yet upgraded to 10, but it is on my list of things to do for the PCs I have at home.
In my opinion, the default should be to preserve existing settings. I know other technically astute commenters do not see it as a big deal, however, as I see it, it is this kind of behavior that has gotten M$ into trouble in the past. In this context, I see it as them getting an unfair boost for edge - even if it is a better browser, and if there is some sort of monetary boost for M$ to be doing this, then I see this as just one step short of coercion. As one other commenter said, the people who will be the most bothered by this are those who are not technically astute - like my father-in-law.