Abrowser, et al; Privacy across New Private Windows not Honored?

https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history says:
Cookies set in private windows are held temporarily in memory, separate from regular window cookies, and discarded at the end of your private session (after the last private window is closed).

My understanding is that private windows can access "regular window" cookies and that any cookie saved while privately browsing can be accessed from any private window (whatever the tab), but it is erased "at the end of your private session (after the last private window is closed)".

Hello Magic Banana,

I tried first non-private instance, made pref. setting change (-> ..suggestion "off") on DDG site settings page. Then launched new Private window. The pref. setting change was not set (i.e. ..suggestion was still set to "on" in Private browser window).

Then tried the opposite, Private first and then non-Private with the same result. But non-Private to non-Private and Private to Private, the settings are remembered.

My question is "why?". Why have anything set up to be seen across Private browser window instances?
Doesn't it defeat the notion of 'tracker' blocking?

If I log into an account somewhere from one Private window, then go to another site in another Private window, what can be known by the other site? Or, I am on one site, then go to another on a new Private window instance and log in. Can my login, or keystrokes be watched or known?

Or, I am shopping the big A, and I don't want them to know everything I am considering at the moment, so I open a new browser instance. Unfortunately, it is not new at all. I wonder if it ought to be?
Thanks.

Hello,
Thanks.
Magic Banana, that linked page does provide an answer to the concerns I raised.
I probably was not the first to express those.

I'll have to see on what browsers that addon can be employed (other than firefox unaltered).

Note: I tried the profile creation and change in a mozilla browser, but 'switch'-ing profiles closes all windows and relaunches the browser.
I could not find the profile manager in Abrowser to see if it did the same behavior.
Chaosmonk, my trial of both Abrowser (which btw still has the font rendering problem) and another mozilla browser differ in that.
Neither were seeing in either direction from Private to non-Private and the reverse. They only saw across the same type of instance.
Also, I was thrown off for a couple of seconds because once an instance of Abrowser Private was launched, it would not allow me to launch a non-Private window, even from the terminal without '--private'. On the other hand, a Private window could be launched from the menu 'File' drop down in the non-Private browser instance. As you mentioned, it is intentional. Might I were it otherwise.

Hello Magic Banana,

Another look at that site re: containers revealed that Abrowser already has the function built in.
Apparently, it is not as function full as the addon, but I went ahead and made the :config changes as noted. Containers seems to be working. New 'container' tab instances do not remember the page preferences from existing tabs. Nice.
There is some stated nuance to this that I will have to discover through some more useage.
I wonder if there is some downside to be discovered, since this is not set up to function as a default option in settings, but rather obscured.

Hello Magic Banana,
Yes, the Container options are there in Abrowser's preferences.
I have added the 'tab' button to 'tab bar' menu, and my standard 'Menu' bar under File's dropdown menu has a "New Container Tab" entry and sub-menu as well.
The 'tab' button will reveal the container options with either an extended Left click and hold (a quick left click opens a regular tab), or with an instant right click.

However, rather than adding an Extension to get and enable Container Tabs, I just changed some of the ':config' settings according to the instructions near the bottom of the page you provided the link to above.

Here is the section from that page:

"For advanced users: You can also enable Containers without the Multi-Account Containers extension, by changing some preferences in the Configuration Editor (about:config page). Note that you will get a better user experience by installing the extension but, if you choose not to, you can set privacy.userContext.enabled to true, privacy.userContext.ui.enabled to true and privacy.userContext.longPressBehavior to 2 in about:config."

I went ahead and tried it even though I am not an advanced user and it seems to work. I won't know what user experience I am missing out on though.