Why won't Firefox die?

[Dave Horsfall]

Firefox 55.xx on Sierra.

Before anyone whinges about this not being a MacPorts bug, I've never 
observed it on my Debian box.

When FF starts gobbling up memory and CPU time (all too often) I restart 
it, except that it's taken to leaving a zombie behind (although the little 
white dot has gone from the icon):

76731   ??  R      7:02.92 /Applications/Firefox.app/Contents/MacOS/firefox

It does not respond to HUP/INTR/TERM, only a KILL.

It this the Mac port in error, or a more generic one?  I don't know about 
the rest of you, but FF seems to be going down the toilet lately, with new 
defects, sorry, "features" being introduced before existing ones have been 
fixed.

-- 
Dave Horsfall DTM (VK2KFU)  "Those who don't understand security will suffer."