Thank you tshering for your explanation !
Actually the "kbmenupngs" folder is in the root directory and now I've set KSM to start always. Then if I tap on "start nikel" in KSM and then I tap on "switchtokoreader", I simply return in KSM instead of displaying the file browser with all files readable by the KOReader...
About the point 1 (frontlight) the value was unsufficient to notice the subtle difference between on and off: increasing it to the max value of 39 was fixing my problem.
Please what is the easiest way to return in the file browser while I'm reading a book ?
Last but not least, I don't understand which files or directories should be put in the ".adds" directory instead of the root one !