It just going to come up with whatever selector that fits the element under your cursor. On obfuscated sites it's usually some kind of generated mess, randomized classes, randomized element names. Not only they're not constant, they change between reloads of the page.

Not sure how things are on Facebook, my point is that element picker is not a silver bullet.

We need a next generation of adblocker with computer vision that can look at the page and recognize banners visually