We are doing feature detection on a site I'm building, but the client insists users with older browsers be shown an upgrade page ("sorry, your browser is outdated, please visit XYZ site to download a newer version") once before they can use the site. After they've seen the upgrade page, the site will not show it again to that user.
This will be a temporary redirect if the user agent is an old browser. The redirect will only be issued if a certain cookie is not on the user's system ("HasSeenUpgradePage" or something)
I suggested a top banner on each page, or a once-only top banner, but my client insists and I like getting paid.
I'm concerned it'll break the site for people viewing in privacy mode.
Is there something I can do to recognize a user's session in privacy mode? (I'd expect closing the browser and reopening it to result in the user seeing the upgrade page again, that's no problem)
Thanks!