Reply received from Buffer:
"Yes, you are right that it is a Buffer cookie. We have the same string of letters at the end of the link to download our extension: "https://chrome.google.com/webstore/detail/buffer/noojglkidnpfjbincgijbaiedldjfbhh?hl=en." This is string is how Chrome recognizes our extension. When you search your Cookies area for "Buffer," this odd cookie should also pop up.
I'm sorry for the oddness with it, and I just wanted to make sure you knew that it's a legitimate cookie so you don't have trouble in the future."