Have read the previous chain pertaining to this problem, the concensus seems to be "remove MS Essentials". Upgraded Windows 7 pro to W10 last November, since which I've had intermittent "Thunderbird not responding" events. Open Thunderbird, it downloads mail OK, but from then on it's pot luck. "Not respondings" can occur on a/ Message deletion b/ During message composition c/ at "send" (fortunately, closure saves it as Draft) Only solution - close (= windows searching for solution") then reopen, often numerous times before full functionality. Read previous thread, checked my settings/Program Files I don't have Windows Essentials, but do have Defender. So, disabled Defender (I also have Avast) "Thunderbird not responding" problem persists !! Not a compacting problem - do that every time it asks - and have many GB of unused memory. System is clean of malware and auto-upfated.