The further discussion about how computers are used has reminded me that I use the following Firefox extensions to protect myself while browsing the web:
Adblock Plus
uBlock Origin
Ghostery
Privacy Badger
Decentraleyes
HTTPS Everywhere
Facebook Container
Even if you insist you never visit any dodgy sites, it’s worth using some form of browser protection because you never know when a third party (advert provider, usually) is going to inject malicious content to a trusted site.