vanadium: enforce firefox as default program for text/html

nix/homeModules/common/firefox.nix

@@ -1,5 +1,12 @@
-{pkgs, ...}: let
+{
+  pkgs,
+  config,
+  lib,
+  ...
+}: let
   inherit (pkgs) nur;
+
+  cfg = config.programs.firefox;
 in {
   programs.firefox = {
     # https://mozilla.github.io/policy-templates
@@ -87,4 +94,14 @@ in {
       ];
     };
   };
+
+  xdg.mimeApps = lib.mkIf cfg.enable {
+    enable = true;
+    associations.added = {
+      "text/html" = ["firefox.desktop"];
+    };
+    defaultApplications = {
+      "text/html" = ["firefox.desktop"];
+    };
+  };
 }