You can put 2fb.me before any URL to make it shareable to Facebook. This works on sites that don't have share buttons like Reddit and Twitter.
Tweets are shareable too, add 2fb.me before the Tweet status URL and it will share that tweet.
2fb.me/amazon.com – shares the Amazon website to Facebook, works with any product page.
2fb.me/twitter.com/shareU/status/936797191540109313 – shares the Twitter status to Facebook.