Firefox and Ad Blocker are running locally on my PC but they don't have a way to reach out anywhere and say "don't send that". This site sends an ad and it goes through the ISP to this computer where Ad Blocker intercepts it and doesn't display it, but the damage is done - that data counts toward my monthly usage.
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My understanding is that is how the blocker works. It does not stop the ad from the server, it only stops it from displaying.
FWIW
