Web: Over the years, you have probably clicked the Like button on several Facebook pages in which you are no longer interested. Facebook Cleanser performs a quick sweep to clean up your news feed.
Head to the webapp, log in with Facebook, and give it some time. You'll see a full list of all the pages you have liked in your entire Facebook history. Click the "Like" button again to unlike any page that you no longer want associated with your account, which is an important step in cleaning up your online presence.
Cleanser took some time to show all the pages I have liked. Giving it half an hour was the magic number for me to see the full list, but you will see a shorter list within seconds.
You can also view this list on Facebook, but it's a little more cumbersome. Go to Activity Log, click "Likes" in the sidebar, and choose "Pages and Interests". It populates only the most recent activity and it updates older Likes only when you scroll down — so you'll have to keep scrolling endlessly until the time you started using Facebook to get a full list.
Of course, this is only going to clean up Pages you liked. If you want to thoroughly declutter your Facebook news feed, we have a guide for that too.