Firefox Prevent Ad Measurement
summer 2024 Firefox added “privacy-preserving ad measurement” and turned it on by default. Many say this is better than invasive tracking so you should turn it on but if you want no tracking at all and don’t accept it as “inevitable” you can turn it off. Go to Settings > Web Site Advertising Preferences and deselect “Allow web sites to perform privacy-preserving ad measurement”.
This should be enough but people are reporting finding it is re-enabled after updates, so to stop the scumbags completely you need to also change the settings in About:config so that if it does try to send data it will go nowhere.
in about:config
search and modify the following two properties to a loopback address: 127.0.0.1
toolkit.telemetry.dap_helper
toolkit.telemetry.dap_leader
This will prevent any conversion reports from being sent.