Using extensions will increase the memory footage as they need to store their filters and databases and they override builtin Firefox Tracking Protection (they get control in an earlier stage). Builtin Firefox Tracking Protection will always be active, so won't add extra memory. Extensions can only work via JavaScript APIs and thus will likely be slower than builtin means and every request needs to be scanned by the extension to see whether it needs to be blocked. *https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop