Add firefox.etp & smartblock.firefox.etp to Mozilla Whitelist

Signed-off-by: celenity <celenity@celenity.dev>

Author: celenityy

base/whitelists/mozilla.txt

@@ -125,6 +125,11 @@ tracking-protection.cdn.mozilla.net
 tracking-protection.prod.mozaws.net
 tracking-protection.stage.mozaws.net
 
+## Internal domain, used by Firefox for SmartBlock placeholders
+### https://searchfox.org/mozilla-central/source/browser/extensions/webcompat/lib/shims.js
+firefox.etp
+smartblock.firefox.etp
+
 ## MITM Detection Priming
 mitmdetection.services.mozilla.com