You will be able to 'react' to the content, shown in posts, but not actually 'dislike' it. The new button is called the reactions button. All you'll have to do, is click on the standard like button to get seven options of empatheic emoji styles to choose from. You are already well-acquainted with the thumbs up option, but now you can also opt to say love, haha, yay, wow, sad, and angry. We assume yay is better than thumbs up, but we're just guesssing here.
According to Tech Crunch, whom Facebook first spoke to, "the pop-up feature will first start out as a test in two markets only, Spain and Ireland, before it decides whether to tweak it and/or how to roll it out further."
It was also reported that the new set of reactions will appear across both mobile and desktop versions of the app and on all posts in the News Feed from friends, Pages/accounts you follow, or advertisers.
Interestingly, at the time being, you only know how many people liked your post, but in the future, you will also be able to tell which people loved it, or found it sad.
Also, Facebook will give you no option to turn off these responses. Once they're there, you're stuck with them, whether you like them or not. So, let's give it some time and see how people react to the new reactions.