I'm seeing a website able to track my browsing between private and regular browsing sessions. When I search for items on amazon.com in a private browsing session (without logging into the website) and later close the private browsing session, I am shown these and related items in "Related to Items You've Viewed" section on amazon.com in a regular browsing session (in which I am logged into the website). My initial guess was that amazon.com was tracking my behaviour based on my IP address, so as to enable it to recognize my search history despite cookies being deleted from the private browsing session. However, I experimented with using the website in a private browsing session while logged into a VPN (Private Internet Access) (without logging into my Amazon account), closing the session and logging out of the VPN, and opening amazon.com in a regular session (after restarting the browser). I still observed the same behaviour, i.e. amazon.com showed me the items I had searched for in the private browsing session. I repeated the same test in Chrome a few times, and Amazon did not show search history from Chrome's incognito mode in the regular session, with or without VPN usage, suggesting that in Firefox, Amazon may have been able track my usage based on residual cookies/cache or similar from the private browsing session. FYI I'm using a few addons in Firefox, but none related to Amazon.