Bookmarking sites in a browser, privacy question

[gorg86]

Hello,

I got a glimpse at a management console for car dealers on a selling platform, and there was a statistics tab about visitors etc. including:
-amount of visitors
-amount of people who printed out the advert
-amount of logged in people who put the advert on their watchlist
-amount of people who bookmarked the advert in the browser
etc.

All of this can be explained easily, including the amount of people who printed out the page (because the browser requests the print version of the site),
but what I don't understand is how that website can see how many people bookmarked a specific page, those are NOT people who are logged in and put the site on a watchlist,
those are just bookmarks in the browser.
You could explain this maybe for smartphone users that use chrome and that data got synced to the cloud and sold off to the website owner, but it does not explain how that would work
on a desktop computer using Firefox.
When you bookmark a page in FF you see a thumbnail of the page below the button on the top right (by default), is that a unique request that can be interpreted by the website?

Thx

[Screenager]

Other than a javascript "Bookmark us" button. There is no way to tell. Alltough there is a lot of money made in selling 'aggregate data' which basically means we make up a bunch of bullshit and find someone who needs this data to reinforce their ego and sell it to them.