At least it was a small scale experiment and not something that rolled out to the whole install base, I use Firefox on a couple of computers and didn't see it myself. But should you really need user feedback to know that inserting an overlay that looks like in-page ad content is a bad idea?
They are completely out of their depth and not fit for their job.
Trust me, they're politically aware of what they are doing, and are only gauging outrage now. Give it some time and they'll figure out how to leverage the outrage, as they did before.
Never let a good crisis go to waste, and all that.
Mozilla got rid of their founder, Brendan Eich, for donating to a California initiative against gay marriage. Now we see what that costs us.
Having the best pool of workers in the world aren't going to make a difference[1] if they are working for power-mongers who use outrage to achieve a coup.
The reverse is not true - having fewer skilled workers to choose from can be irrelevant when they are working for someone who is focused on goals that are aligned to the user.
IOW, there's no point in having the absolute best and the brightest people employed by self-serving schemers who wanted to use firefox as a vehicle for their political/virtuous ambitions.
There might be, however, a point in having "only" the 90% best people employed towards making firefox better.
[1] And, it looks like it didn't make a difference.