So... what kind of nonsense do I need to disable in about:config this time?
What a pointless question; how can any of us know what your individual preferences are like? Mozilla aims to ship a default configuration that works well for a large number of users. Of course there'll be people -- like yourself, apparently -- who'd prefer some things to be configured differently, but what you'd like changed is entirely up to you. Maybe you should be grateful Firefox offers (quite a lot of) customisa…
Are you sure they're trying to ship what works best for most people? I've not read that anywhere. If they really wanted people to have a choice, they wouldn't be adding configurations that can't be switched on/off through they're preferences menu - like for example, that crazy bar they just added a couple of releases ago - oh.. and which apparently you are not allowed to switch off no more, not even through about:config, according to sibling comment. Also, they have a track record of breaking old configuration options quite often through updates.
I am grateful by what they offer - just not sure they're not sneakily changing course, similar to what chrome did.