With the new Privacy Regulation in the EU, and since Mozilla is distributing FireFox globally, would there soon be a way to sue Mozilla in the case of privacy invading updates?
But for that, you need Mozilla to actually violate privacy or for them to perform a contract with another company and then not ensuring enough that the data is handled correctly by that contractee. The pure speculation that on a technological level, it would be possible for your privacy to be infringed by Mozilla or through their use of Pocket, Cliqz, Google Analytics or indeed this extension (though I still don't understand how it's supposed to be privacy infringing in the first place), does not suffice to successfully sue them.
Mozilla ensures legally towards its users that their privacy is not infringed upon in their Privacy Statement and just as well has legal contracts ensuring that Read It Later Inc. (former developer of Pocket, now owned by Mozilla), Cliqz GmbH or Google Inc. don't infringe upon this user privacy either. So, legally Mozilla is not touchable here.
If you can prove that they do not comply with their Privacy Statement or the GDPR, or do not do enough to ensure that their contracted companies comply with those, then you can again sue them. But you are were already perfectly able to sue them for violating their own Privacy Statement for as long as they've existed.
I'm not saying sueing Mozilla is what should be done. But I'm very much interested if it will be possible.