Earlier quoted context omitted.
Doing this will make it trivially easy to fingerprint and track you on the web, as the set of people who use non-defaults like this list is 0.000001% of the total possible user space for their area, and your IP address probably only changes rarely or never A better way to protect yourself is to use a browser with tracking protections on by default, and leave the settings alone. You may see a few more ads but you’ll b…
I don't see how using containers in Firefox or auto-deleting cookies would have any negative effect here. None of the cache deletion/isolation addons should inject any Javascript into the page or alter headers in any way, so they shouldn't be detectable to sites you visit. So in terms of unique behavior, all that site isolation means is that you're going to hit caches more often and be missing cookies. I mean, sure,…
Websites can only make inferences based on the absence of unique cross-site cookies if you are configuring your browser in non-default ways. If all Firefox 85+ users are partitioning, then any inferences drawn from that behavior do not increase your trackability — and it could well decrease it, as those Firefox 85+ users will be joining the swarm of Safari users whose browser has already done the same sort of partitioning for a couple years.
Multi Account Containers are an oddity, and alone they would not be particularly distinguishable from a multi-user computer (which, at a home residence, could be unusual; many people don't have User Accounts on a shared device). However, when combined with cross-container tracking infection (such as URL parameter tags designed to survive a transition to another container, e.g. fbclid or utm_*), it's possible to identify that a user is using containers, which is a very rare thing and not available by default, thus increasing risk of being tracked.
UBlock Origin allows far too much customization for me to prepare any clear reply there. I imagine it is possible to run UBO with a ruleset that only interferes with requests to third-party adservers, without letting the first-party know that this is occurring. I doubt, however, that a majority of UBO users are running in such a circumspect mode. Adblocking often requires interfering with JavaScript in ways that are easily visible to the first-party (who has a vested interest in preventing ad fraud).
Fingerprinting is a known defense against fraudulent clicks, so there's a lot to puzzle over there. But I definitely don't like to take active steps to make myself stand out from others. I'm annoyed that I'm tracked a little on the web, but I'm indistinguishable from the general pool of "users with default browser settings" today. That's a type of protection that addons can't provide. I'm not wholly certain what I think yet, but happily the browsers continue advancing the front of protection forward, so maybe by the time I decide it won't matter anymore. YMMV.
ps. I'm glad to see your much more nuanced consideration of this balance, and I wish that more took your careful approach here when recommending "privacy" setups to others.