refactor(nixos): simplify Firefox configuration

configs/nixos/modules/desktop/apps/firefox.nix

@@ -5,11 +5,9 @@
   pkgs,
   ...
 }:
-# Firefox as the desktop browser: stock mainline, hardened and de-monetized by policy.
+# Configures Firefox as the desktop browser.
 let
   cfg = config.modules.desktop.apps.firefox; # NOLINT(let_order)
-  firefoxAddons = inputs.firefox-addons.packages.${pkgs.stdenv.hostPlatform.system};
-  user = config.user.name;
 in
 {
   options.modules.desktop.apps.firefox = {
@@ -19,19 +17,20 @@ in
       type = lib.types.str;
       default = "1.0";
       description = ''
-        Firefox UI and page scale, passed to `layout.css.devPixelsPerPx`.
+        Scales Firefox UI and page content.
-        Override it on hosts that need a larger browser scale, such as small
+
-        high-DPI laptop panels.
+        Sets `layout.css.devPixelsPerPx`.
+        Use a larger value for high-DPI displays.
       '';
     };
   };
 
   config = lib.mkIf cfg.enable {
-    home-manager.users.${user} = hm: {
+    home-manager.users.${config.user.name} = hm: {
       programs.firefox = {
         enable = true;
 
-        # Enterprise policies: enforced and unchangeable from the browser UI.
+        # Applies policies that users cannot change in Firefox.
         policies = {
           DisableTelemetry = true;
           DisableFirefoxStudies = true;
@@ -40,7 +39,7 @@ in
           DontCheckDefaultBrowser = true;
           DisableFirefoxAccounts = true;
 
-          # Strip the monetized surfaces from the new-tab page.
+          # Removes sponsored content from the new-tab page.
           FirefoxHome = {
             SponsoredTopSites = false;
             SponsoredPocket = false;
@@ -49,23 +48,19 @@ in
         };
 
         profiles.default = {
-          isDefault = true;
-
           extensions = {
-            packages = with firefoxAddons; [
+            packages = with inputs.firefox-addons.packages.${pkgs.stdenv.hostPlatform.system}; [
               ublock-origin
               proton-pass
               sponsorblock
             ];
 
-            # The Nord chrome theme is a declared extension setting, so home-manager
+            # Home Manager overwrites Nord theme changes made in Firefox.
-            # owns the extension-settings store, overwriting runtime changes to it.
             force = true;
           };
 
-          # Stylix's Nord mapping paints the selected address-bar result a
+          # Stylix uses a near-white selection background.
-          # near-white grey, leaving its light text unreadable. Darken that one
+          # Use the Nord selection color because its text stays readable.
-          # highlight to the Nord selection grey, from the same scheme.
           extensions.settings."FirefoxColor@mozilla.com".settings.theme.colors.popup_highlight =
             let
               c = hm.config.lib.stylix.colors;
@@ -77,32 +72,26 @@ in
             };
 
           settings = {
-            # Scale the UI and page by a fixed factor.
-            # Left at auto (-1), Firefox reads the panel's 1.5x and inflates its
-            # whole chrome while point-sized apps stay put.
-            # A shade under that brings it into line without dropping to true
-            # 1:1, which reads too small at this DPI.
             "layout.css.devPixelsPerPx" = cfg.uiScale;
 
-            # Auto-enable the sideloaded Firefox Color add-on carrying the Nord
+            # Enables Firefox Color after Firefox sideloads the add-on.
-            # chrome theme, which Firefox otherwise leaves disabled.
             "extensions.autoDisableScopes" = 0;
 
-            # Sponsored surfaces the policies above do not reach.
+            # Removes sponsored content outside Firefox policies.
             "browser.urlbar.suggest.quicksuggest.sponsored" = false;
             "browser.newtabpage.activity-stream.showSponsored" = false;
             "browser.newtabpage.activity-stream.showSponsoredTopSites" = false;
           };
 
           search = {
-            # Declaring search overwrites Firefox's own engine list wholesale,
+            # Home Manager replaces the engine list when this setting is enabled.
-            # so engines added later in the UI do not survive a rebuild.
+            # Engines added in Firefox do not survive a rebuild.
             force = true;
             default = "ddg";
 
-            # The general-purpose commercial engines, hidden to leave a lean
+            # Hides commercial search engines.
-            # DuckDuckGo-and-Wikipedia list. They stay reachable through bangs.
+            # Bangs still reach these engines.
-            # An engine carrying only metaData is treated as a builtin.
+            # Entries with only `metaData` configure Firefox built-in engines.
             engines = {
               google.metaData.hidden = true;
               bing.metaData.hidden = true;
@@ -114,8 +103,7 @@ in
         };
       };
 
-      # Nord chrome for the one profile, applied through the Stylix-managed
+      # Applies the Nord theme through Stylix's Firefox Color add-on.
-      # Firefox Color add-on that colorTheme enables.
       stylix.targets.firefox = {
         enable = true;
         profileNames = [ "default" ];
@@ -133,8 +121,8 @@ in
         };
       };
 
-      # Firefox writes profiles.ini itself on first launch, so home-manager is
+      # Firefox creates `profiles.ini` on its first launch.
-      # told to own the file rather than fail activation refusing to clobber it.
+      # Force replacement during Home Manager activation.
       home.file."${hm.config.programs.firefox.configPath}/profiles.ini".force = true;
     };
   };