Well, the same was true for the so heftily discussed Looking Glass extension.
It did not do anything, unless you manually switched on an about:config value. And if you did, then all it did, was flip some random words on webpages upside down.
Which is a relatively arbitrary criteria to be so categorical about.
No, I don't like it either to have eastereggs in my software that wasn't just put there for the fun of it, and rather was also motivated to some degree by a continued commercial relationship. But if this commercially motivated easter egg helps to gather more money to improve the software, which itself is non-commercial, and is as harmless as Looking Glass, then I do not see a problem with that.
And let me repeat that, if it is as harmless as Looking Glass.
I do not see a reason to categorically exclude any sort of commercially motivated thing from the browser. Even including some actual ads would in my opinion not be unthinkable, given that they get enough money for it and have effective ways to do good with that money, while especially also taking into account that users will get pissed off by it and leave the browser, effectively slimming the ability of Mozilla to do good.
If you take everything into account, you can be morally on the good side without having to resort to never doing things from certain categories.
It did not do anything, unless you manually switched on an about:config value. And if you did, then all it did, was flip some random words on webpages upside down.