I haven't seen the series, but I also find the idea of ARGs interesting.

What it's being discussed here is not if the addon is interesting or not, it's the fact that Mozilla, a supposedly freedom and privacy advocate has installed something in all of our computers, without our knowledge or permission as a publicity stunt for a different company and, when found out, the best explanation we've received is "Oops! You guys shouldn't have seen that".

Personally, I'd much rather have them make money through these sort of small tidbits than rely entirely on Google money. If they actually were on a slippery slope and selling out user privacy or whatnot for profit, I'd also not think of it to be acceptable, but to me there's always a clear distance from that slope in anything that Mozilla does, by ensuring that no privacy violations or anything along those lines happen. Specifically with things that people will spin conspiracy theories about and bring out the pitchforks, they always go the extra mile to ensure that really nothing is actually bad about it.