This is a chrome browser extension you can install to hide the "laughing" emoji reaction from facebook.
Because almost everyone who uses this emoji uses it to signify mockery, not to appreciate jokes. It's the default tool people use in the absence of a "dislike" button. It is most often affixed to opinions you disagree with, to indicate "I'm laughing at you because you are stupid and I want you to feel small." I'm sure if there was a "respectfully disagree" reaction, people would use that, but there isn't, so people use this as a sort of "rudely disagree" button. It makes facebook a much less pleasant place.
Mostly. There are a few edge cases I don't handle, but the main cases (reactions to posts and comments in the main feed) are handled pretty reliably. If you spot a case where I missed one, feel free to open a bug report or send a pull request, I'd like to improve this over time.
Download this repository as a zip file and then load it as an unpacked extension. Eventually I'll get it added to the chrome store.