How do I stop FirefoxCP process preventing sleep? If I open my activity monitor and show the 'preventing sleep' column I notice that I have five process called FirefoxCP Web Content and one of those has the preventing sleep set to true.
How can I make my computer sleep when I ask it to?
Things I've tried

disabled all add ons
To manually initiate a sleep on the mac and override 'Preventing Sleep' applications run
pmset sleepnow
in the terminal
(you may find something in man pmset that can alter the settings, I performed a quick look but couldn't find anything)