diff --git a/README.md b/README.md
index d67ed93874865c2411e63bbcdc1106d17d370208..7cb0c67b5b49d252bc2fbf0a7edf96ae768d3af0 100644
--- a/README.md
+++ b/README.md
@@ -23,6 +23,8 @@ It's possible to:
 
 The extension can be start and stop via the button on the top right.
 
+The rules are active in private window mode but you can't use the configuration window in this mode.
+
 The code is opensource under Mozilla Public License 2.0