An alternative to PithHelmet is Glimmer Blocker. It works quite well for me and it doesn't hack into the system. I don't use Firefox much so I don't know how effective it is there but, if I understand the way that it operates correctly, it should work.
Jon
macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365
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