Same issue as already written here:
Selenium 3.2.0 crashes FireFox 52 during driver.quit () @Win 7 Home Premium and GeckoDriver 0.14.0
Does this problem mean all Win7 computers or some others? What about Win8 and Win10?
Here you can find a workaround for this problem.
Many thanks to the guys who found him - they deserve loans:
https://github.com/mozilla/geckodriver/issues/517#issuecomment-286375220