This is a weird one. On the one hand, we have Mozilla, the last remaining browser company not sucking at the teat of either Google or Apple and we all expect for Mozilla to somehow generate enough money to pay enough employees to stay competitive on the other hand we have the users who expect them not to do anything to try and leverage their userbase to create financial independence.
The problem with Mozilla remains the same problem that they've had for a while. Mozilla doesn't acknowledge the symbiotic relationship it has with its community and the community always over reacts, which means there's a chasm where simple things should be easy but they're not.
Take this for example, Mozilla only had to have a public facing discussion about this and then go and do it anyway.
Sometimes paying lip service works. But since they didn't, you have people like OP who feel like something nefarious is happening and in the end Firefox users lose out as things like donations being pulled hurt.
Mozilla already shows ads, as do all the other browsers, however unlike the other browsers, you have a fully functioning uBlock that can and will remove anything that the preferences don't cover.
Is this just cosmetic or is there a real benefit to the lack of corner?