Firefox/Chrome/Safari: If you aren't able to keep up with the Olympics live and forced to wait until primetime to watch events on replay, browser extension Olwimpics blocks spoilers by censoring relevant words.
Olwimpics censors words such as Olympics, sports, games, gold, silver, bronze and any kind of distances in metres, as well as names of sports, like swimming and gymnastics. It's certainly not foolproof though -- some words such as medal(s) and different events like freestyle and backstroke aren't censored. Popular athletes' names are also not censored. Because of this, a few spoilers can get by, but you can easily just close out a page when you come across a slew of bars.
It's also worth noting that Olwimpics will block other, non-Olympic sports as well, so be aware of this if you visit other sports sites frequently.