added "Statistics" part

README.MD

@@ -35,6 +35,9 @@ https://www.youtube.com/watch?v=RdV8DBW5b0g
 ## More info
 See the extension help in the options page for more detailed information about the options, and technical notes.
 
+## Statistics (Firefox)
+https://addons.mozilla.org/en-US/firefox/addon/single-file/statistics/?last=90
+
 ## Known Issues
 - All browsers:
   - For security reasons, you cannot save pages hosted on https://chrome.google.com or https://addons.mozilla.org.