First: Hey, yes, they fu**ed-up! But: I can understand why…
Because, personally, I'd really liked such a thing. Hey, yes, I like #MrRobot and it promotes the same values as Mozilla. And an #ARG can be funny, including such a "intentionally creepy" text in your add-ons and so on. It's really a geeky thing when you get hidden signs for a TV show, you like, in your browser or so. As Mozilla puts it, it "was intended to be fun".
So I think this may have been a funny/geeky idea of the marketing dep.
Unfortunately, it is not. Because when you participate in these Studies, you accept some A/B tests or similar feature tests to improve the browser. What you certainly do not want is advertisement. And this is advertisement. As said, I'd really enjoy it, but I can understand other people don't. I'd also not like to have ads for other things in my browser… It's also bad from a security perspective, of course. No one wants to see a strange add-on (with deliberately strange texts) in your browser, when you open it.
So, yes, that went pretty bad. And they had alternatives: Just use the snippets at about:newtab e.g. On the other hand this would not have been so fun as a real "immersive" ARG.
However, some facts easily get lost when people complain about that. First, ONLY US users were affected. This does not necessarily make it better or worse, but it shows how people are overreacted when they disable Firefox Studies to prevent that add-on from getting installed, if they are located in Germany or so. Secondly, the add-on DID NOT collect user data. And the distribution process has been stopped "[w]ithin hours". The FAQ at https://support.mozilla.org/en-US/kb/lookingglass now explicitly says, you have to "opt-in", i.e. install an add-on, to activate it. Yet again, this does not make the initial problem better, but it shows Mozilla cares for that and reacts to user feedback. Finally, however, the reason to do the initial act, was NOT money. No, it just was not. "This was not a paid promotion"… Of course, they did not do it without a return service (@whoismrrobot promoted Firefox on Twitter), but I believe them, when they say, the did it because of the show itself.
To conclude, I think they made a mistake, indeed. And no, this must not happen with a company of that size and one of the largest browser vendors. And you do not have to forgive them for that. It was a mistake (likely, of the marketing dep.). I don't want to compare that situation to other browsers, but at least you have the choice to disable Firefox Studies from the beginning; after it happened, Mozilla reacted and, what may be the most urgent point for many: It did not collect user data. (So that whole thing was NOT a !privacy problem.)
They regret it and we can hope they'll do better in the future. And, no, you don't have to uninstall your browser, just because of that. You likely were never near that add-on installation, and even if, the add-on would not have collected any data, so it was not as bad as some may sound it like…