fix(firefox): use theme new tab background

nixos/home/firefox/custom.css

@@ -38,4 +38,7 @@ slot {
   :root:not([chromehidden~="toolbar"]) #PersonalToolbar {
     margin-top: -103.5px !important;
   }
+  :root[privatebrowsingmode]:not([chromehidden~="toolbar"]) #PersonalToolbar {
+    margin-top: -106.5px !important;
+  }
 }

nixos/home/firefox/firefox-gx.nix

@@ -17,6 +17,9 @@ stdenvNoCC.mkDerivation {
     # Personal changes
     sed -i 's/var(--fuchsia))/var(--purple))/' ./chrome/components/ogx_root-personal.css
 
+    substituteInPlace ./chrome/components/ogx_root-personal.css \
+      --replace '../images/newtab/wallpaper-dark.png' "$out/chrome/images/newtab/private-dark.png"
+
     mv ./Extras/Tab-Shapes/ogx_tab-shapes.css ./chrome/components
     rm ./user.js
     mv ./Extras/Tab-Shapes/user.js ./

nixos/home/firefox/main.nix

@@ -9,6 +9,7 @@ in
     ".mozilla/firefox/matt/chrome/components".source      = "${firefox-gx}/chrome/components";
     ".mozilla/firefox/matt/chrome/icons".source           = "${firefox-gx}/chrome/icons";
     ".mozilla/firefox/matt/chrome/images".source          = "${firefox-gx}/chrome/images";
+    ".mozilla/firefox/matt/chrome/userContent.css".source = "${firefox-gx}/chrome/userContent.css";
   };
 
   programs.firefox = {
@@ -21,7 +22,6 @@ in
         ${builtins.readFile "${firefox-gx}/chrome/userChrome.css"}
         ${builtins.readFile ./custom.css}
       '';
-      userContent = builtins.readFile "${firefox-gx}/chrome/userContent.css";
       extraConfig = builtins.readFile "${firefox-gx}/user.js";
 
       settings = {