Comment 7 for bug 1967963

I have the same problem in Xubuntu, fwiw. Firefox is unable to set itself as the default browser no matter how many times I restart it and click "Set as Default Browser" in its settings menu or its pop-up reminders complaining that it's not the default. And clicking on links in Thunderbird opens up in Chrome. However XFCE settings *thinks* it's the default, if I open it up and look.

I eventually gave up and re-installed via apt using the mozilla.org repo, and that version has no problem setting itself as default, so it's clearly a snap packaging problem.