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As others have pointed out, it's an advertising technique called retargeting. Here are some of the technical details of how exactly it is done(Facebook's implem

As others have pointed out, it's an advertising technique called retargeting. Here are some of the technical details of how exactly it is done(Facebook's implementation might differ somewhat from this, but overall concept is same) /* DSP - Demand side partner (Entity which works with someone who wants to show their ads) SSP - Supply side partner (Entity which works with some who have potential space on web to show ads) / 1. When you visited Amazon.com, one of the DSP associated with them drop a cookie on your system to uniquely identify you as a user. Let's call it cookiexyz. 2. When you end up on Facebook.com, their SSP also drops a cookie on you, let's call it cookieabc. 3. Now only thing remaining is to determine cookiexyz and cookieabc are same users. 4. To do that, SSP requests a bid from Amazon's DSP(among others). While doing that, it calls one of the DSP's url(bid tag) which sends cookiexyz in request headers and sends cookieabc in query params. This uniquely profiles the user which DSP stores in their system and next time user requests a bid again, they can serve them ads based on preferences based on cookiexyz. In other words, info that your looked at some shoes on Amazon.com / disclaimer: I work as a dev in one of the Advertising partner for Yahoo and Bing. */

oelmekki 9y ago
Thing is, OP mentions using two different browsers, which is why it's surprising. I guess there's still the possibility that a cookie was added months before that and that "tainted" browsing was forgotten. But it's still worth wondering if some other identification mechanism could be at play.
- theweirdone 9y ago
  Or, facebook(https://www.facebook.com/business/learn/facebook-ads-reach-existing-customers https://www.facebook.com/business/learn/facebook-ads-reach-e...) matches this cookie to your fb account in their system. Then making this information available across the browsers is trivial. Now, to actually think of implementation, I can't even imagine the amount of data they need to store(and clear in LRU manner) to make this work.
- saluki 9y ago
  I'm sure they are tracking/matching by cookies, ip, FB logins, geolocation, etc . . . by combining those it's pretty easy to serve up the right ad, most of the time.
dhimes 9y ago
It's weirder that that. I was notified via a Facebook ad that my Navionics subscription to charts from Asia expired. I only use Navionics as an ios App.
- shostack 9y ago
  That's not weird. Navionics presumably had your email address. They then likely uploaded that as part of a list of customers into what FB calls a "Custom Audience List" and promoted some post to that audience.

oelmekki 9y ago

Thing is, OP mentions using two different browsers, which is why it's surprising. I guess there's still the possibility that a cookie was added months before that and that "tainted" browsing was forgotten. But it's still worth wondering if some other identification mechanism could be at play.

theweirdone 9y ago
Or, facebook(https://www.facebook.com/business/learn/facebook-ads-reach-existing-customers https://www.facebook.com/business/learn/facebook-ads-reach-e...) matches this cookie to your fb account in their system. Then making this information available across the browsers is trivial. Now, to actually think of implementation, I can't even imagine the amount of data they need to store(and clear in LRU manner) to make this work.
saluki 9y ago
I'm sure they are tracking/matching by cookies, ip, FB logins, geolocation, etc . . . by combining those it's pretty easy to serve up the right ad, most of the time.

dhimes 9y ago

It's weirder that that. I was notified via a Facebook ad that my Navionics subscription to charts from Asia expired. I only use Navionics as an ios App.

shostack 9y ago
That's not weird. Navionics presumably had your email address. They then likely uploaded that as part of a list of customers into what FB calls a "Custom Audience List" and promoted some post to that audience.