I just discovered the problems I've been having for 4 months were caused by OldNewExplorer.
 
	I had the latest version installed on Windows 10 Pro x64.
 
		All 64-bit variants of Firefox freeze forever after a few minutes even if I don't use them
	
	
		Task Manager freezes immediately on launch
	
	
		Explorer was incredibly unstable and crashed every few minutes
	
	Uninstalled and all my problems have gone.