diff --git a/modules/programs/firefox.nix b/modules/programs/firefox.nix
index e63a72670..6a3ab656c 100644
--- a/modules/programs/firefox.nix
+++ b/modules/programs/firefox.nix
@@ -444,6 +444,15 @@ in {
                 '';
               };
 
+              privateDefault = mkOption {
+                type = with types; nullOr str;
+                default = null;
+                example = "DuckDuckGo";
+                description = ''
+                  The default search engine used in the Private Browsing.
+                '';
+              };
+
               order = mkOption {
                 type = with types; uniq (listOf str);
                 default = [ ];
@@ -675,8 +684,8 @@ in {
         };
 
       "${profilesPath}/${profile.path}/search.json.mozlz4" = mkIf
-        (profile.search.default != null || profile.search.order != [ ]
-          || profile.search.engines != { }) {
+        (profile.search.default != null || profile.search.privateDefault != null
+          || profile.search.order != [ ] || profile.search.engines != { }) {
             force = profile.search.force;
             source = let
               settings = {
@@ -767,12 +776,18 @@ in {
                     # engine if it's not in profile.search.engines
                     ${profile.search.default} =
                       profile.search.engines.${profile.search.default} or { };
+                  } // {
+                    ${profile.search.privateDefault} =
+                      profile.search.engines.${profile.search.privateDefault} or { };
                   };
                 in sortEngineConfigs (mapAttrs buildEngineConfig engineInput);
 
                 metaData = optionalAttrs (profile.search.default != null) {
                   current = profile.search.default;
                   hash = "@hash@";
+                } // optionalAttrs (profile.search.privateDefault != null) {
+                  private = profile.search.privateDefault;
+                  privateHash = "@privateHash@";
                 } // {
                   useSavedOrder = profile.search.order != [ ];
                 };
@@ -794,14 +809,21 @@ in {
                 profile.path + profile.search.default + disclaimer "Firefox"
               else
                 null;
+
+              privateSalt = if profile.search.privateDefault != null then
+                profile.path + profile.search.privateDefault
+                + disclaimer "Firefox"
+              else
+                null;
             in pkgs.runCommand "search.json.mozlz4" {
               nativeBuildInputs = with pkgs; [ mozlz4a openssl ];
               json = builtins.toJSON settings;
-              inherit salt;
+              inherit salt privateSalt;
             } ''
               if [[ -n $salt ]]; then
                 export hash=$(echo -n "$salt" | openssl dgst -sha256 -binary | base64)
-                mozlz4a <(substituteStream json search.json.in --subst-var hash) "$out"
+                export privateHash=$(echo -n "$privateSalt" | openssl dgst -sha256 -binary | base64)
+                mozlz4a <(substituteStream json search.json.in --subst-var hash --subst-var privateHash) "$out"
               else
                 mozlz4a <(echo "$json") "$out"
               fi
diff --git a/tests/modules/programs/firefox/profile-settings-expected-search.json b/tests/modules/programs/firefox/profile-settings-expected-search.json
index ceee27ee6..f17a0b91e 100644
--- a/tests/modules/programs/firefox/profile-settings-expected-search.json
+++ b/tests/modules/programs/firefox/profile-settings-expected-search.json
@@ -67,8 +67,10 @@
     }
   ],
   "metaData": {
-    "current": "DuckDuckGo",
-    "hash": "BWvqUiaCuMJ20lbymFf2dqzWyl1cgm1LZhhdWNEp0Cc=",
+    "current": "Google",
+    "hash": "IRmKVSQlAYnvLO8kdZyNUR/g5hzVn4++T0PLPGm+kZk=",
+    "private": "DuckDuckGo",
+    "privateHash": "BWvqUiaCuMJ20lbymFf2dqzWyl1cgm1LZhhdWNEp0Cc=",
     "useSavedOrder": true
   },
   "version": 6
diff --git a/tests/modules/programs/firefox/profile-settings.nix b/tests/modules/programs/firefox/profile-settings.nix
index 6529a1bb2..94fa9436e 100644
--- a/tests/modules/programs/firefox/profile-settings.nix
+++ b/tests/modules/programs/firefox/profile-settings.nix
@@ -75,7 +75,8 @@
         id = 3;
         search = {
           force = true;
-          default = "DuckDuckGo";
+          default = "Google";
+          privateDefault = "DuckDuckGo";
           order = [ "Nix Packages" "NixOS Wiki" ];
           engines = {
             "Nix Packages" = {