Another "great idea" from the Mozilla folks: today they decided to install an Extension named "Looking Glass" with a description of "MY REALITY IS JUST DIFFERENT THAN YOURS" on a bunch of people's Firefox installs. The extension flips certain words upside-down, inserts words into websites, and sends an extra HTTP header to three specific sites, among other things.
It's apparently part of a Mr. Robot ARG. They've already expanded the extension's description to have actual information after users started asking support questions, filing bugs, and speculating about malware.
I'm not sure they wanted a good way to teach people how to turn off telemetry and opt-in random user studies, but they certainly found one.