actually fix prefs this time

debugged this in repl instead of just throwing shit on the wall and
hoping it works like the last version of this function

modules/nixos/multimedia/web/firefox/preferences.nix

@@ -1,10 +1,11 @@
 let
-  mkPreferences = prefs: builtins.concatStringsSep
+  mkPrefs = prefs: builtins.concatStringsSep 
     "\n"
-    (builtins.mapAttrs
-      (name: value: "user_pref(\"${name}\", \"${value}\");"));
+    (builtins.attrValues
+      (builtins.mapAttrs
+        (n: v: ''user_pref("${n}", "${v}");'') prefs));
 in 
-  mkPreferences {
+  mkPrefs {
     prefs = {
       "browser.urlbar.suggest.topsites" = false;
     };