I hope so. It's more likely something infected Firefox itself, and didn't get into the OS. But when I checked the modem logs, it happened up to a couple of months after the fact. That's worrying.
What's even more worrying is that a couple of websites told me I had an IP address that didn't match my home IP, but would provide the correct one if I refreshed the page a couple of times. So some kind of covert proxy or VPN type of thing was happening.
I ended up just wiping everything, to be safe. Still a bit paranoid though.