Wow, you've been busy, you uninstalled Firefox and everything, that is above and beyond the call of duty.
Firefox usually does leave behind the profile folder when it's uninstalled so that users don't lose their bookmarks, etc. I'm not 100% certain, but I don't think the profile folder being left behind would cause Spybot to detect it as an open browser, though.
Not to be distracted from the 4 unimmunized hosts file entries, but just to go over some things about Firefox I find a bit odd, and I've been unable to find anything about them online anywhere.
I notice that says System. If I am remembering this right (and it's very possible I'm not, so don't let this alarm you.), when Spybot detects Firefox open browser before immunization, the name in brackets is the name of the account that it is being run on, while looking in Immunization itself shows the profile name instead. In that case, it would look like Spybot might be possibly running from an account named System. I don't imagine the Windows account you are logged into now is called System, is it? I also find it odd that when you went to shut down Firefox the first time, it wasn't available in Task manager, and I also find it odd that after you uninstalled Firefox Spybot still detected Firefox as an open browser. This could well be a technical problem with Firefox, I'm sure. And you have ran scans and they have come up clean, so that is good. And everything is running okay on your computer? You haven't noticed anything different happening lately?