I am running both core and firefox from stable. Yes, I know it normally works as it should, as I can create a clean user, login, and things work fine. It is something to do with my primary account’s setup. But I don’t know what, as I have no idea what firefox is doing when it hands something off to “Url Handler Script”. I assume this is some helper somewhere that sneaks the URL out of containment via DBUS or some interface, but I can’t find any useful info to help me diagnose where things are failing or why Firefox is unaware that things are failing. The only feedback is the message in system.log, which is only helpful at pointing me to something inside the snap (so some setting in my Firefox profile, which I pulled in from from the non-snap install).
If it is unclear, this is any time Firefox needs to hand things off to an external process, such as clicking a PDF link. Firefox gives me the choice to save it, or hand it off to something else, and that something else is “Url Handler Script”.