I don’t know if this is an issue with Comodo or Malewarebytes, I suspect the latter.
I recently had my free version of Malewarebytes upgrade to a 7 day free trial version. Now when I run Firefox in my Comodo Sandbox the file called MBAMservice that belongs to Malewarebytes is using 50% to 100% of CPU.
It only happens when I run Firefox in the Comodo Sandbox option from from Comodo tray icon on the desktop. When Firefox is run not sandboxed then it does not happen. It appears that MalewareBytes does not like Comodo Sandbox.