diff --git a/hosts/backwards/modules/firefox/default.nix b/hosts/backwards/modules/firefox/default.nix
index 96c291e..f438cf0 100644
--- a/hosts/backwards/modules/firefox/default.nix
+++ b/hosts/backwards/modules/firefox/default.nix
@@ -46,6 +46,12 @@ in
 
       package = wrapped;
 
+      # Pin the legacy profile location. The default changed to the XDG path
+      # (`$XDG_CONFIG_HOME/mozilla/firefox`) for stateVersion >= "26.05";
+      # keep the old `~/.mozilla/firefox` so the existing profile isn't
+      # stranded (migrating would require moving the profile dir by hand).
+      configPath = ".mozilla/firefox";
+
       profiles = {
         alex = {
           id = 0;