Skype does questionable stuff
I've noticed summat odd when running a previous version of skype, that when browsing with FF and with skype on-line, FF was suddenly trying to serve up stuff which was blocked via the hosts file. This stopped when skype was off-line, and URLs were blocked as normal (FF did not have any skype extensions in it, BTW).
It looks like skype decided to act a proxy server, though I know not how. Or why.
One post mentioned that in similar situations the HTML source in his browser would get extra tags linked to skype (though this didn't happen with me).
Big-time not ok, so now skype runs in its own VM.
I don't know if newer versions have such dubious behaviour, but caveat emptor anyway.