For a while I was changing my browser back and forth between firefox versions. Every single time windows 10 would detect that change and 'protect' me from it by opening the default programs control panel and setting the default browser to Edge.

It makes sense if they want the default browser to require user confirmation to change. But setting it to Edge in the meantime? That's just being rude and anti-customer.

Well that I didn't know. What I meant was shipping with a given browser which I see as their right. What you describe is naughty and not good at all.

I think it has a habit of changing itself to default even after the user sets something else as the default. Minor annoyance though compared to the overall pain of using a windows machine.

"Minor" depends on whom you ask: each time this happens, MS generates n angry support tickets...for me, not for themselves, of course: "the computer is broken again and I have lost all bookmarks and sign-in data, why did you break it again?!?" (The good news is, of course, that nothing is "lost" except for the default browser flag: resetting to FF fixes it...until next time)

As far as I am concerned, they can. But they are not bloody supposed to change it again, after I have changed it to something of my choosing. I am sick and tired of "yeah, so you have set your default browser to FF, but we know better than you what you want; so we have reset it again on yet another Patch Tuesday. Admit it, YOU WANT THE E!" (Consent, what consent?)

Does this only happen with certain configurations or something? I've been using Windows 10 since it came out and can't really remember this happening to me

As far as I'm aware this has to do with the fact that major updates are being delivered in a manner that's basically equivalent to a full reinstall, causing a lot of settings to get reset to defaults. This update method is particularly common for the insiders, but still happens from time to time on the general builds: anniversary update, creator's update and such.

Makes sense.

Makes sense for people who want nightlies and constant flux. Makes absolutely zero sense for production machines.

No idea; I am not MS's QA, and only have a handful of configs. Plus it doesn't even happen consistently on the configs that I do have.