I think you might be in a bubble of you think the average person is using container extensions. There aren't even that many average people using Firefox anymore, least of all any extensions beyond adblockers (which still only reach at most 20% in general, including the all round more average Chrome users)
<off-topic-rant> Add to that there aren't even any container extensions that work well: the official Mozilla one doesn't support management of domain lists, and the best alternative (Containerise) is still limited and poorly supported (has outstanding bugs with things as simple as the www prefix). As for the individual site-specific options, the Google one is an all or nothing affair; there is no way to separate your traffic within Google's ecosystem, nor outside it: there's effectively two "zones", similar up Private Mode.
I wouldn't recommend containers to an average user in their current state
I just asked "who knows what VPN means" in IM group of non tech savvy folks, most under 35. No one knows.
Perhaps among us Firefox users that's different but certainly "most people under 40 today" wouldn't know even what VPN means.
VPNs are heavily marketed to regular consumers these days. Mostly for region shifting or vague privacy/security benefits.
I'm not sure "watching" is the correct word.
> those with any consciousness of their own vulnerability want to take action to minimize their surface area
This is a pretty small minority, as demonstrated by the number of people that continue to use Google and Facebook properties by choice (refering to their actual services, not their pervasive tracking around the Internet at large)
> firefox with container extensions
As a more-technical-than-average person, my experience is that attempting to get all Google services running in a specific google-only firefox container is a non-trivial and extremely painful experience, as there doesn't appear to be a way to simply add *.google.com to the 'always open in this container' list, so each subdomain needs to be added individually. And then youtube.
> adblockers
Adblocks can break the check-out flow on multiple ecommerce sites. "Don't shop there" doesn't fly when that's the only online outlet that has the shoes she wants. What's the workaround? Spend a while working out what's causing the flow to break, and find a way to explicitly whitelist that domain for that site? Nope, just disable the adblock entirely and hope you remember to re-enable it once you're done.
When these people say "surveillance" they mean they think that Facebook magically hears it when they say something out loud and they start seeing ads for it. We engineers overestimate the awareness average user has about technology.
Not "magically" - they don't trust their device. And can you blame them? Their device likely isn't trustworthy in so many different ways.
Hell, when accelerometers can be repurposed as rudimentary microphones, and when just about every modern device/app defaults to maximum "yes please track me," I tend to be paranoid myself!
To give an example, after the recent WhatsApp PR crisis because of the change of toc, I see a whole bunch of my contacts changed to Telegram. They could have chosen Signal but no. They switched from an end-to-end encrypted app to an unencrypted app! That's what paranoia gets you unless you know what you're doing. I've pretty given up on the average user on these matters.