diff --git a/nixos/modules/programs/firefox.nix b/nixos/modules/programs/firefox.nix
index ed874cad74e4..8229affb1ad9 100644
--- a/nixos/modules/programs/firefox.nix
+++ b/nixos/modules/programs/firefox.nix
@@ -313,7 +313,9 @@ in
             old.extraPrefsFiles or [ ]
             ++ cfg.autoConfigFiles
             ++ [ (pkgs.writeText "firefox-autoconfig.js" cfg.autoConfig) ];
-          nativeMessagingHosts = old.nativeMessagingHosts or [ ] ++ cfg.nativeMessagingHosts.packages;
+          nativeMessagingHosts = lib.unique (
+            old.nativeMessagingHosts or [ ] ++ cfg.nativeMessagingHosts.packages
+          );
           cfg = (old.cfg or { }) // cfg.wrapperConfig;
         }))
       ];