If you take a look at the installed extensions of your version of Firefox right now, you may notice a new extension called Looking Glass listed among them.
You can display all user installed extensions on about:addons. Chance is very high that you did not install Looking Glass, and the description "MY REALITY IS JUST DIFFERENT THAN YOURS." does not really reveal anything about the extension.
I doubt it will make any difference but I used the feedback function in my Firefox browser at Help | Submit Feedback (https://qsurvey.mozilla.com/s3/FirefoxInput/) to tell Mozilla what I thought of this blatant abuse of the Firefox (Shield) Studies and suggested that they automatically disable the setting at Privacy & Settings | Firefox Data Collection and Use | Allow Firefox to Install and Run Studies in future Firefox releases.
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32-bit Vista Home Premium SP2 * Firefox ESR v52.5.2 * NS Premium v22.11.2.7 * MB Premium v3.3.1
"You can prevent Mozilla from installing studies in Firefox by opening about:preferences#privacy, and removing the checkmark from "allow Firefox to install and run studies".
There was a discussion about Mozilla automatically enabling the setting for opting in to these Shield studies back in August 2017 in the Tech Outpost at Mozilla Testing New Default Setting for Firefox Telemetry Collection but I didn't think they'd be stupid enough to install a third-party extension in Firefox without warning users.
I checked my Firefox ESR v52.5.2 browser and the setting for Shield studies still hasn't appeared (yet ) in my Privacy, Security or Advanced | Data Choices options.
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32-bit Vista Home Premium SP2 * Firefox ESR v52.5.2 * NS Premium v22.11.2.7 * MB Premium v3.3.1
Don't trust anyone, is my motto !
Like Imacri, I'm still using the latest ESR version.
) in my Privacy, Security or Advanced | Data Choices options.