diff --git a/modules/programs/firefox/mkFirefoxModule.nix b/modules/programs/firefox/mkFirefoxModule.nix
index 307d39305..046d55d06 100644
--- a/modules/programs/firefox/mkFirefoxModule.nix
+++ b/modules/programs/firefox/mkFirefoxModule.nix
@@ -483,25 +483,11 @@ in
                     (
                       bookmarks:
                       if bookmarks != { } then
-                        lib.warn
-                          ''
-                            ${cfg.name} bookmarks have been refactored into a submodule that now explicitly require a 'force' option to be enabled.
-
-                            Replace:
-
-                            ${moduleName}.profiles.${name}.bookmarks = [ ... ];
-
-                            With:
-
-                            ${moduleName}.profiles.${name}.bookmarks = {
-                              force = true;
-                              settings = [ ... ];
-                            };
-                          ''
-                          {
-                            force = true;
-                            settings = bookmarks;
-                          }
+                        {
+                          force = true;
+                          _legacySettings = if builtins.isList bookmarks then "a list" else "an attribute set";
+                          settings = bookmarks;
+                        }
                       else
                         { }
                     )
@@ -1028,7 +1014,59 @@ in
         ++ optional (cfg.vendorPath != null) ''
           Using '${moduleName}.vendorPath' has been deprecated and
           will be removed in the future. Native messaging hosts will function normally without specifying this path.
-        '';
+        ''
+        ++ lib.flatten (
+          lib.mapAttrsToList (
+            name: profile:
+            lib.optional (profile.bookmarks._legacySettings != null) (
+              let
+                legacySettingsExample =
+                  if profile.bookmarks._legacySettings == "a list" then "[ ... ]" else "{ ... }";
+              in
+              lib.hm.deprecations.mkDeprecatedOptionValueWarning {
+                option = modulePath ++ [
+                  "profiles"
+                  name
+                  "bookmarks"
+                ];
+                old = profile.bookmarks._legacySettings;
+                replacement = "`${
+                  lib.showOption (
+                    modulePath
+                    ++ [
+                      "profiles"
+                      name
+                      "bookmarks"
+                      "settings"
+                    ]
+                  )
+                }` with `${
+                  lib.showOption (
+                    modulePath
+                    ++ [
+                      "profiles"
+                      name
+                      "bookmarks"
+                      "force"
+                    ]
+                  )
+                } = true`";
+                details = ''
+                  Set `force = true` to acknowledge replacing existing custom bookmarks.
+
+                  Replace:
+                    ${moduleName}.profiles.${name}.bookmarks = ${legacySettingsExample};
+
+                  With:
+                    ${moduleName}.profiles.${name}.bookmarks = {
+                      force = true;
+                      settings = ${legacySettingsExample};
+                    };
+                '';
+              }
+            )
+          ) cfg.profiles
+        );
       targets.darwin.defaults = (
         mkIf (cfg.darwinDefaultsId != null && isDarwin) {
 
diff --git a/modules/programs/firefox/profiles/bookmarks.nix b/modules/programs/firefox/profiles/bookmarks.nix
index 25fd23483..78a4b468e 100644
--- a/modules/programs/firefox/profiles/bookmarks.nix
+++ b/modules/programs/firefox/profiles/bookmarks.nix
@@ -84,6 +84,12 @@ in
   ];
 
   options = {
+    _legacySettings = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      visible = false;
+    };
+
     enable = mkOption {
       type = with types; bool;
       default = config.settings != [ ];
diff --git a/tests/modules/programs/firefox/bookmarks-legacy-attrset-warning.nix b/tests/modules/programs/firefox/bookmarks-legacy-attrset-warning.nix
new file mode 100644
index 000000000..187409dae
--- /dev/null
+++ b/tests/modules/programs/firefox/bookmarks-legacy-attrset-warning.nix
@@ -0,0 +1,50 @@
+{
+  config,
+  ...
+}:
+
+let
+  cfg = config.programs.firefox;
+in
+{
+  imports = [
+    (import ./setup-firefox-mock-overlay.nix [
+      "programs"
+      "firefox"
+    ])
+  ];
+
+  home.stateVersion = "26.05";
+
+  programs.firefox = {
+    enable = true;
+    profiles.default.bookmarks = {
+      "Home Manager" = {
+        url = "https://wiki.nixos.org/wiki/Home_Manager";
+      };
+    };
+  };
+
+  test.asserts.warnings.expected = [
+    ''
+      Using `programs.firefox.profiles.default.bookmarks` as an attribute set is deprecated and will be
+      removed in a future release. Please use `programs.firefox.profiles.default.bookmarks.settings` with `programs.firefox.profiles.default.bookmarks.force = true` instead.
+
+      Set `force = true` to acknowledge replacing existing custom bookmarks.
+
+      Replace:
+        programs.firefox.profiles.default.bookmarks = { ... };
+
+      With:
+        programs.firefox.profiles.default.bookmarks = {
+          force = true;
+          settings = { ... };
+        };
+
+    ''
+  ];
+
+  nmt.script = ''
+    assertFileExists "home-files/${cfg.profilesPath}/default/user.js"
+  '';
+}
diff --git a/tests/modules/programs/firefox/bookmarks-legacy-warning.nix b/tests/modules/programs/firefox/bookmarks-legacy-warning.nix
new file mode 100644
index 000000000..5c18ab437
--- /dev/null
+++ b/tests/modules/programs/firefox/bookmarks-legacy-warning.nix
@@ -0,0 +1,51 @@
+{
+  config,
+  ...
+}:
+
+let
+  cfg = config.programs.firefox;
+in
+{
+  imports = [
+    (import ./setup-firefox-mock-overlay.nix [
+      "programs"
+      "firefox"
+    ])
+  ];
+
+  home.stateVersion = "26.05";
+
+  programs.firefox = {
+    enable = true;
+    profiles.default.bookmarks = [
+      {
+        name = "Home Manager";
+        url = "https://wiki.nixos.org/wiki/Home_Manager";
+      }
+    ];
+  };
+
+  test.asserts.warnings.expected = [
+    ''
+      Using `programs.firefox.profiles.default.bookmarks` as a list is deprecated and will be
+      removed in a future release. Please use `programs.firefox.profiles.default.bookmarks.settings` with `programs.firefox.profiles.default.bookmarks.force = true` instead.
+
+      Set `force = true` to acknowledge replacing existing custom bookmarks.
+
+      Replace:
+        programs.firefox.profiles.default.bookmarks = [ ... ];
+
+      With:
+        programs.firefox.profiles.default.bookmarks = {
+          force = true;
+          settings = [ ... ];
+        };
+
+    ''
+  ];
+
+  nmt.script = ''
+    assertFileExists "home-files/${cfg.profilesPath}/default/user.js"
+  '';
+}
diff --git a/tests/modules/programs/firefox/default.nix b/tests/modules/programs/firefox/default.nix
index f3379b44f..082a2231e 100644
--- a/tests/modules/programs/firefox/default.nix
+++ b/tests/modules/programs/firefox/default.nix
@@ -1,5 +1,7 @@
 { lib, ... }:
 {
+  "firefox-bookmarks-legacy-warning" = ./bookmarks-legacy-warning.nix;
+  "firefox-bookmarks-legacy-attrset-warning" = ./bookmarks-legacy-attrset-warning.nix;
   "firefox-config-path-explicit-legacy" = ./config-path-explicit-legacy.nix;
   "firefox-config-path-explicit-xdg" = ./config-path-explicit-xdg.nix;
   "firefox-config-path-xdg-default" = ./config-path-xdg-default.nix;
diff --git a/tests/modules/programs/firefox/profiles/bookmarks/attrset.nix b/tests/modules/programs/firefox/profiles/bookmarks/attrset.nix
index bd157a0a6..9d45517be 100644
--- a/tests/modules/programs/firefox/profiles/bookmarks/attrset.nix
+++ b/tests/modules/programs/firefox/profiles/bookmarks/attrset.nix
@@ -72,6 +72,25 @@ in
       };
     }
     // {
+      test.asserts.warnings.expected = [
+        ''
+          Using `${lib.showOption modulePath}.profiles.bookmarks.bookmarks` as an attribute set is deprecated and will be
+          removed in a future release. Please use `${lib.showOption modulePath}.profiles.bookmarks.bookmarks.settings` with `${lib.showOption modulePath}.profiles.bookmarks.bookmarks.force = true` instead.
+
+          Set `force = true` to acknowledge replacing existing custom bookmarks.
+
+          Replace:
+            ${lib.showOption modulePath}.profiles.bookmarks.bookmarks = { ... };
+
+          With:
+            ${lib.showOption modulePath}.profiles.bookmarks.bookmarks = {
+              force = true;
+              settings = { ... };
+            };
+
+        ''
+      ];
+
       nmt.script = ''
         bookmarksUserJs=$(normalizeStorePaths \
           "home-files/${cfg.profilesPath}/bookmarks/user.js")