Running Enpass 5.6.5 on Windows 7 (firefox and Vivaldi Browser with enpass add on) I realized that my memory was eaten up by literally hundreds of Enpasshelper.exe processes.
Each process consuming slightly more memory than the previous one ending wihth 100MB per process. The number of processes exceeded the number of browser tabs by far and the problem worsent over time. After a fresh boot everythings was normal , after half a day the number of processes built up and consumed the memory.
I assume some relation to 5.6.5 as I could not see this behavior with the version before and/ or to the browser add on (vivaldi with enpass chrome extension, which I started using). I therefore removed the add ons in vivaldi and firefox to see if the behaviour changes.
Killing the EnpassHelper.exe processes freed up the memory and did no further harm.