Yes, they allow full avoidance of any potential data collection through the browser, if they remove the collection features.

Mozilla would need to change their licensing terms to prevent forks from being able to remove things like that, and forks could just use the last version of the code before the license change and just backport new features.

Also Firefox is fully open source, unlike chromium which relies on a closed source binary blob in the middle. Some chromium forks have replaced the binary blob with open source code, but the default is for chromium forks to have a nice chunk in them controlled by google that no one can deeply inveatigate what it does. Firefox does not have this issue.

Mozilla can’t hide any potential data collection in Firefox due to the full open source nature (unlike chrome forks). They also can’t stop fork devs from stripping out any data collection functions. And as of today, they have not introduced any data collection that is not supremely anonymized, and they have not introduced any data collection that cannot be opted out of through the browser settings (and about:config).