Butter does not collect, store or send any personal data. It has no account, no analytics, no telemetry and no crash reporting.

All settings, counters and cached filter lists are kept in Firefox's local extension storage on your computer and never leave it.

The only network requests Butter makes are downloads of filter lists from their publishers (EasyList, Fanboy, Peter Lowe, abuse.ch, uBlock Origin) when lists are updated. These requests carry nothing about you beyond what any download does. Automatic updates can be turned off in Butter's settings; the built-in core list keeps working offline.

Butter changes some Firefox privacy settings (through the browser.privacy API) only to protect you, and hands them back to Firefox when you turn the option off or remove Butter.