I never use firefox for anything but when I'm 1) in private mode and 2) on a VPN. I purposefully only use it for this so there can be no overlap with my main browser.Today I started getting ads on my main browser for something I was searching for in my firefox + VPN combo. I was googling for something quite specific and medical. Think cosmetic foot surgery or something.How is this possible?  I can't even think of a technical means. Perhaps window size or some other metadata? Perhaps leaving my main browser open but not browsing caused an ajax request to go out over the VPN IP that linked the two?I thought I was pretty safe with a VPN for this sort of stuff, but now I'm questioning what the point is and if there is any hope of browsing the internet with any semblance of privacy.