"Facebook Messages has a feature that tells you when a chat recipient has seen a message. This "read receipt" is, in true Facebook fashion, both nifty and unsettling. And it brings with it tons of potential for abuse. Unfortunately, there's no built-in method to opt out. Facebook's privacy interface has undergone change upon change, yet some needed controls simply don't exist—and these days consumer privacy depends heavily on control. Luckily, the developers over at Crossrider have an extension, Chat Undetected, that disables the read receipt feature. The extension is available for Chrome, Firefox, Internet Explorer, and Safari. By nature of its popularity, Facebook is inviting developers to customize users' experiences and create useful tools. We're hoping Facebook adopts a policy that allows its users to innovate, create, and—in the spirit of Facebook—hack. Currently, an overly vague Terms of Service has led Facebook to shut down helpful add-ons like Fluff-Busting Purity, which let users configure what news items were shown to them. As FB Purity's developer notes, many of his users stuck around Facebook only because their experience was tailored to their liking."