• Firefox Nightly 77.0a1 (2020-04-21) (32-bit)
• Windows 10 Home (version 1909, OS build 18363.778)

For some reason, I'm unable to set Nightly as my default browser on my Windows 10 laptop. I get the prompt asking if I'd like to set Nightly as default upon starting the browser OK, and following that flow takes me to the right place in Windows settings. The problem is that Nightly doesn't appear as an option in the list of choices (see attached screenshot). All other browsers appear ok.

1. Is the release build also 32-bit?
2. Can you go into regedit and export the key
   HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet
   and attach that here? Also the HKEY_CURRENT_USER version of the same path if there's anything in there.

Thanks.

Is the release build also 32-bit?

Release build is 75.0 (64-bit). Reminder for me once this bug is fixed: I should really reinstall my Nightly on Windows so it's 64-bit!

Hope I did this right

(In reply to Alex Gibson [:agibson] from comment #2)

Release build is 75.0 (64-bit). Reminder for me once this bug is fixed: I should really reinstall my Nightly on Windows so it's 64-bit!

Doing that would probably fix this, actually; I'm just trying to see if we can figure out how it happened first.

(In reply to Alex Gibson [:agibson] from comment #3)

Created attachment 9142104 [details]
keys.zip

Hope I did this right

Is that the only thing that's in those StartMenuInternet keys? I was expecting a different Firefox-something and also an IEXPLORE.EXE, and there should be something for Chrome too.

I did just now notice you've got the new Edge, which is making me mighty suspicious; do you know if this problem predates that showing up?

Trying this again

I did just now notice you've got the new Edge, which is making me mighty suspicious; do you know if this problem predates that showing up?

I did just literally install the new Edge today, but I can't be sure if this problem existed before then or not (it's not my primary machine for daily use).

That's perfect, thank you.

You don't have to attach the key, but can you check if HKEY_LOCAL_MACHINE\Software\RegisteredApplications has values for both FIREFOX.EXE and Firefox-EEFEA8717BC47F65 that point to their respective Capabilities keys?

I'm trying to recreate this scenario and see what else might be involved, but so far I haven't managed to reproduce the bug and that's the only other relevant spot I can find.

You don't have to attach the key, but can you check if HKEY_LOCAL_MACHINE\Software\RegisteredApplications has values for both FIREFOX.EXE and Firefox-EEFEA8717BC47F65 that point to their respective Capabilities keys?

Yes, I see entries for both under RegisteredApplications, and both have Data paths that point to Capabilities keys.

Okay, thank you. In that case I am very sorry but I have no idea what's going on; I had always thought those locations were what the default browser menu was built from, and they all seem correct, so likely my understanding of how this works is wrong. Of course the documentation for all of this was never updated for Windows 10. So I think I need to leave this on the backlog to investigate further.
You don't want to wait for me to do that, so to fix this now I'd recommend uninstalling both channels and reinstalling them. The uninstaller doesn't touch profiles so you won't lose any that way, but if you do switch to 64-bit that will change the install paths, so you'll get new per-install profiles and you might have to have the profile manager set the old one as the default.

Thank you - I've reinstalled Nightly and I can now set it as default again.

The severity field is not set for this bug.
:agashlin, could you have a look please?

For more information, please visit auto_nag documentation.

As this might be related to new Edge we might want to leave this open. I'm marking S3 for now, if we can reproduce it (or if anyone disagrees) S2 might be more appropriate.