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).
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).