In the newest versions of Firefox, a feature called "Enhanced Tracking Protection" will be enabled by default. This security feature is mainly targeting 3rd party trackers, who will track a visitors movement between multiple websites.
Mouseflow Tracking is Not Affected
Enhanced Tracking Protection won't affect Mouseflow tracking behavior, because we don't use third party cookies when recording a visit. So even with this new feature enabled, a Firefox user will still be recorded normally.
Opt Out is Affected
Ironically Enhanced Tracking Protection does affect users ability to Opt Out of being recorded by mouseflow.
What happens when you click the Opt Out button is that a 3rd party cookie is set in your browser telling Mouseflow not to record this user - but because Firefox is now disabling these 3rd party cookies this is no longer possible in Firefox.
Excluding yourself from being recorded
It's still possible to exclude your own and your teams visits to your site from being recorded by Mouseflow by excluding your IP addresses.