firefox: suport passff as an addon

though i don't yet have it wired to my password store

hosts/common/programs/firefox/addons.nix

@@ -51,6 +51,11 @@ in
         package = pkgs.firefox-extensions.open-in-mpv;
         enable = lib.mkDefault false;
       };
+      passff = {
+        package = pkgs.firefox-extensions.passff;
+        nativeMessagingHosts = [ pkgs.passff-host ];
+        enable = lib.mkDefault false;
+      };
       sidebery = {
         package = pkgs.firefox-extensions.sidebery;
         enable = lib.mkDefault true;