How do I stop Windows 10 from resetting my default browser?

Question

Windows 10 keeps resetting my default browser to Microsoft Edge. I am trying to run Firefox Developer Edition as my default browser. The reset happens randomly, maybe once every week or two, but it is rather annoying.

I talked to Microsoft support and they wanted me to turn off Windows Update (!). I declined. I suspect it may be related, though.

My Windows Update history shows that the last update was KB3213986, applied on 2017-01-12. I noticed that my browser had been reset on 2017-01-16.

Has anyone else encountered this problem? Is there a fix?

Solution

The default browser is set in the Registry under

HKCU\SOFTWARE\Classes\http

and

HKCU\SOFTWARE\Classes\https

These user settings take precedent over those in HKEY_CLASSES_ROOT, which may be ignored.

You could right-click on the command key and change permissions so it is less likely that Windows will mangle your settings on the next update.

You can also make a small .reg file, exporting those settings, so the next time MS does foul it up, you just need to merge it back into the Registry.