Windows 11 Default Apps: Firefox and Thunderbird

Recently I moved from a Thinkpad X1Yoga running Mint and Windows 10 to a Thinkpad P14s running Kubuntu and Windows 11 Pro 25H2. On the Win11 side (which behaves differently from Win10), there are installation issues affecting both Firefox and Thunderbird. Win 11 '''Settings''' lists: under ''Apps > Installed apps'' * . . . (other apps) * Mozilla Firefox (x64 en-US) 154.0 * Mozilla Maintenance Service 153.0 * Mozilla Thunderbird (x64 en-US) 153.0.2 * . . . (other apps) under ''Apps > Default apps'' * . . . (other apps) * Firefox * Firefox * . . . (other apps) That is, ''Default apps'' lists Firefox twice (though not as "Mozilla Firefox"), but Thunderbird not at all. This causes two problems: # It's not clear which Firefox to choose for browser protocols. # There is no Thunderbird to choose for mail-related protocols, Can someone tell me why the Installed apps and Default apps list differ, and how to set the appropriate defaults for Firefox and Thunderbird? Thanks, John