Disable the Firefox notification pop-in (?) "add (website.name) as a handler for web+nostr links?" which has no option to never ask you again by adding to your (profile dir)/user.js (or about:config which gets saved to prefs.js): 

    user_pref("network.protocol-handler.external.web+nostr", false);

This pop-in happens when a Nostr webapp uses the javascript function "registerProtocolHandler()" [1] to add itself as the preferred webapp. You can extend this to any "protocol" known or unknown by just using the name of whatever that webapp is trying to register (there's a list of known types in the footnote link).

#firefox #nostr #webapp

[1] https://developer.mozilla.org/en-US/docs/Web/API/Navigator/registerProtocolHandler