Mmm... well it behaves exactly as if they are still running. I have Firefox set to NOT remember my open tabs after quitting. If I open another program then return to Firefox via the 'recent apps' icon then the tabs are open exactly as before and even the web page position. If, however, I close Firefox on the 'recent apps' popup (it does say 'close all' at the bottom not 'remove' or 'hide') then run Firefox again (don't know any other way to run it but to click on its icon) then it starts up at the home page.
Hang on. Just remembered there's a list of running programs in App Manager - yes, they're all running.