They're trying to find a solution which will allow opening links without needing to install
snapd-xdg-open, until that solution is found, merged into
snapd, and released, you'll need to tell your users to install
snapd-xdg-open. Unfortunately, your users can't do this on any distribution other than Ubuntu; we're going to have to wait for opening links to be possible on more distributions.
That's what I understand from having read the thread, anyway.
Until a solution is found, Corebird (an app I'm asking upstream to provide a Snap for) won't work at all on non-Ubuntu distributions (since you have to be able to open a link in the browser to log in).