Basically, it stops your browser from rendering the sidebar images that spoil the race results. This means that if you miss a race, then you'll have a chance of avoiding spoilers in the subreddit. Beyond that, it also lets you enable or disable this blocking, so if you've seen the race, then you can turn the blocker off. This is a better solution that just turning the subreddit style off, since you can still see the rest of the sidebar's useful information. Notes: As you can see in the screenshots, the icon will turn red when it's on the Formula 1 subreddit, and is blocking spoilers. Likewise, when the icon is black, then nothing is being blocked. The button that pops up after you've clicked the icon says what it will do, not what it's currently doing (ex. clicking on the 'Disable Blocking' button will then disable the blocking). Feel free to contribute with any improvements or bug fixes at the website below.