What he said!
I was pretty scared when I saw all the .sol files in my laptop and where they came from. I deleted the lot and installed the Firefox add-in.
I also blocked some of the sites that had loaded them - they don't come from places I click on: they are linked from those, usually with advertising or tracking as the declared intent. However, given the number of Nigerian gentlemen inviting me to send them large sums via Western Union, and the viruses that bang up against Avast most days, I'd rather not have uninvited and uncontrolled cookies running stuff on my machine.