Restore previous session/tabs

Hi everybody,

Since few days don't know exactly when or why, when I close and reopen Firefox portable the previous tabs are not restored. I checked that the parameter is correctly set in the settings. Maybe it happened after the last update or the one before. To update to a new version I always use the method mentioned in the FAQ (overwrite the previous)
Any idea or verification I could do ? It has always worked correctly since many months