Huzzah, I have now got it working with flash at least, and now about:addons works too!
I'm pretty sure the issues with 4.whatever it was were on a different laptop, at very least on a different install of windows. This install is pretty fresh, really.
And I seriously doubt malware is at fault, as this has only been online via 3G since I got it so i haven't downloaded anything really, just surfing and using Libre Office.