AdBlock + NoScript. The web has been much more tolerable for a long time, thanks to these, and it is always amazing how much noise is on the page when I navigate with an alternate browser.
It would be interesting to know how many devs consider NoScript users when designing websites. (I personally think it's too much effort).
With this policy, I have an awesome track record on my systems with regards to the number of "problems" that have installed themselves on my computer (number = zero, and I do not have AV installed, though I like to temporarily install several AVs and sanity check once every couple years or so; their overhead, constant updates, etc, just are not worth my time).
I don't use NoScript, and have never had anything install itself on any of my machines (to my knowledge at least - and as a dev I actively monitor CPU/Memory so hopefully would notice).