As long as browsers are inherently insecure in regards to fingerprinting protection, the only viable protection is to create an extensive list of known JS fingerprinters.
Additionally one needs to disallow all third party javascript sources by default.
Both strategies are possible with a good content blocker.
These strategies protect against all known and almost all unknown fingerprinting scripts. The only scenario where it doesn't work is unknown first-party scripts, but cross-site tracking is impossible.
Which is the reason Brave is in a good position to do this kind of work. They represent a growing portion of web users, and their research helps to give these users a voice.
This is the downside of what happens when a corporation is not forced to report to someone from outside the corporation, i.e. shareholders, and does not have a direct relationship with their customers.
Usually public corporations are shaped in order to maximize profit and market share. But Mozilla doesn't have to report to someone else, so no one forces them to spend money economically, especially as the Corporation is being controlled by the Foundation who hasn't primarily economics in mind, either.
Additionally, Mozilla has grown exponentially between 2007 and 2014 not only due to a superior product but also because IE was bad, and the web grew exponentially and thus browser usage grew exponentially, too.
Mozilla has inherited a large userbase, and they are in an extremely comfortable position where they can be lazy and do not experience any immediate consequences. Employees earn a lot at Mozilla. Mozilla's own post-mortem of the extension-outage has also hinted at a systemic mismangagement inside what is nowadays a pretty complex entanglement of different groups working on similar stuff while not communicating efficiently.
Mozilla has a leadership problem.
Their business-relationship is not with the users, but the search engines who want to monetize the user base, and due to the exclusive deal with Yahoo for 2015-2019, losing 80 million monthly users within 2 years did not translate to a loss in revenue, revenue actually continued to increase despite user loss. So why care?
I suspect the CEO just resigned because he knows that 2020+ will be extremely difficult for Mozilla, as the Yahoo deal is running out, and for the first time ever mozilla will have to spend more money than they recieve. Lack of money will also be the only real motivation for Mozilla to change fundamentally.
Additionally one needs to disallow all third party javascript sources by default.
Both strategies are possible with a good content blocker.
These strategies protect against all known and almost all unknown fingerprinting scripts. The only scenario where it doesn't work is unknown first-party scripts, but cross-site tracking is impossible.