To a tech-savvy audience its more obvious that private browsing modes don't offer that.
This discrepancy is something that people have genuine concerns about and want to see either more features to protect their privacy, or better transparency in naming/explaining/disclaiming these modes.
Did you actually interview her for this paper? Where'd you find her? Can I ask her a few questions when you're done? I have so much I need to know from the average person.
This warning appears on every tab in the incognito mode, so it is pretty visible.
We wanted the whitepaper to be browser agnostic, this isn't about blaming specific browsers or actions. We wanted to highlight the larger issue that there is a gap in privacy education for a mainstream user and that it is something that members of technical communities can all step up and help with.
As for a special note for the warnings, I would say it is akin to the Terms of Service for websites. Perfectly visible, but never really read and understood.
Further, I'd guess that even if you absolutely trust your SO not to violate your privacy, you might still reasonably distrust the platform they're working on, and you might not want to expose your account credentials on a platform that you don't directly control.
The option I finally chose to go with, is to install firefox on her computer as well. Firefox is for me, Chrome is for her. I'm an FF guy anyway. The main UX problem stands, though, it's too easy to be the wrong person.
Also I get to keep up to date with changes in firefox.
The icons and applications look sufficiently different that there's no confusion about what persona I am in which browser. And I can have all of them up at the same time.