If I understand it correctly, you shouldn't be using any website accounts using Tor browser that you also use outside of it. I really wonder if/how they can make the user properly aware of that in a kind-of super private browsing mode.
you can, and it is still a valuable contribution to the Tor network, since it adds cover traffic. the catch is just that the website you're using will know who you are. I hope that the vast majority of users will understand that if they log in, there is no privacy mode that will save them from the site they log into.
Right, I guess that's good if you want to contribute to the Tor ecosystem, but if you want to browse anonymously, that's no good. Unfortunately, even as a somewhat tech savvy (though in hindsight obviously naive) person, the repercussions of logging in somewhere in Tor Browser weren't immediately clear to me.
I'm not quite sure what you mean by this comment, but if you mean that their approach would be similar to MAC, in the sense that "super private browsing" would have to be enabled in about:config or through an extension: that would make sense.
I know the extension, but what does that have to do with informing users about not using their account when browsing with Tor? Heck, informing users about being able to use different accounts with Multi-Account Containers was already such a hard problem that they opted into shipping it as a separate extension, so it's only used by power users.
How I'd do it is have a warning when using Tor outside of the designated Tor container. That is, encourage the installation of the extension when enabling a "Tor" tab (permanently dismissable of course). Alternatively they could co-opt the private-browsing window (a.k.a. incognito) feature to have a tor-browsing window.
The latter might even be preferred since the former is only at the tab level and probably quite easy to forget whether you are in Tor before entering an address. It appears to be what is suggested in the notes (now that the link is up).
