Legally though Firefox would be allowed to collect this anonymous data from the user by having him/her send the data e.g. to an API endpoint they provide via IP-based communication, they would just not be allowed to associate the data with the IP address of the user submitting the data. In the end, it comes down to trusting the party that collects the data, at least if they don't perform anonymization of the IP address via other means, e.g. by passing the information through a third party proxy server.
BTW, GDPR does forbid to turn on such data collection by default (privacy by default), so they would be required to get the explicit opt-in from the user for that.
My understanding is that many of these details are yet to be settled with GDPR. The case referenced above was not interpreted under GDPR, which has yet to take effect. The definitions of personally identifiable data data rather vague, and precedent has not been set. A quick search showed conflicting opinions, but one perspective to consider is quoted below:
> In addition, businesses should note that Recital 26 to the recently adopted EU General Data Protection Regulation ("GDPR") states that the test for whether a person is "identifiable" (considered in detail above) depends upon "all the means reasonably likely to be used" to identify that person. The CJEU in Breyer did not directly consider the issue of likelihood of identification. If the BRD was not reasonably likely attempt to identify Mr Breyer from his IP address, this could potentially give rise to a different analysis under the GDPR. Consequently, it may be necessary for the CJEU to revisit this issue after enforcement of the GDPR begins on 25 May 2018.
This is a few years old, so if you know of some new decision or regulation that clarifies it would be great to know!
https://www.whitecase.com/publications/alert/court-confirms-...
https://gdpr-info.eu/art-4-gdpr/
Now, you could of course argue that often it's not possible to infer the identity of a person given an IP address (e.g. because it is a dynamically allocated IP address by an ISP or an IP address of a proxy server through which many users connect to the Internet) and therefore store it, it would be very hard to impossible though (IMHO) to ascertain that none of the IP addresses which you store could be used to identify a specific person (what e.g. if there are 5 % static IPs in your data?). This in turn would make treating all of your IPs as non-personal data a risky business to say the least, as there will almost certainly be a way to identify at least some of your users from their IP addresses. The fact that you don't know about a particular way of doing this identification is not relevant for this.
My advice: If you do not use a very robust method for making sure that all the IPs you store are non-identifiable I would recommend not storing them at all (or at least truncating them to 24 bits, which does also not always eliminate deanonymization risk though).
Are you saying that people can not be identified by their IP address?
I think it's important to talk about this issue – especially the importance of not storing it long-term — but from my perspective the real concern is the industry dedicated to linking and sharing your online activity. Without that an IP has little value and with it they can deanonymize most people without using IPs.
Do you have a citation for that broad assertion? My understanding is that this is highly variable across legal jurisdictions and even in Europe, which typically leads the way in privacy, it's not that simple. See e.g. https://www.whitecase.com/publications/alert/court-confirms-... discussing an EU Court of Justice ruling that had two requirements: the ISP can link that IP address to an individual AND the website operator can get that information from the ISP.