Firefox as Flatpak cannot access declaratively configured profile

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1

Hello. I tried follow https://wiki.nixos.org/wiki/Firefox’s home-manager section, the difference is essentially:

{
  programs.firefox.configPath = ".var/app/org.mozilla.firefox/config/mozilla/firefox";

  # using https://github.com/in-a-dil-emma/declarative-flatpak
  services.flatpak.overrides."org.mozilla.firefox".Context.filesystems = ([
    "~/.config/mozilla/firefox/" # paranoid about regular firefox
    "/var/lib/flatpak/extension/org.mozilla.firefox.systemconfig/" # needed?
    "/nix/store" # symlinks to nix store, of course
  ]);
}

However, when running, even with more aggressive permissions:

flatpak run --filesystem=host --filesystem=/nix/store --filesystem=home org.mozilla.firefox

It throws error: “Your Firefox profile cannot be loaded. It may be missing or inaccessible.”, while regular firefox (configPath at default) is fine.

Has anyone succeeded with home-manager + flatpaked-firefox?

2

When trying home-manager on Arch Linux, launching /bin/firefox (not encumbered by permissions like flatpak) throws the same error but ~/.nix-profile/bin/firefox is fine. There seems to be some magic at work for Nix/home-manager.