I believe they are claiming that with the new discoveries it's pointless to keep trying. Whether that's shared with other devs or not probably won't affect their decision:

These three bugs basically ruin the whole point of arkenfox: // sec bugs: offscreencanvas / preconnect / cookie_exceptions

I'm not that familiar with them, but sounds like there's no way to keep a sane balance between usability and privacy, and clearly upstream doesn't help a bit, it's like following the Borg advice "resistance is futile". Battling the privacy fight is not an easy fight I guess. The only hope for those who are non experts as the arkenfox guys is that phoenix keeps up the good work. Overall I pretty much prefer arkenfox over phoenix, but fortunately Librewolf is neither arkenfox nor phoenix, even though they are discussing if they are better based of phoenix the are different projects making different decisions...

I wish frozen fennec didn't die on the attempt, :( The current option is ironfox on LOS/AOSP based/..., and I don't agree with several of their decisions. The amount of filter lists is so stubbornly huge, that there's no time to deselect and/or remove them on low end phones for example, and the whole thing just slow things down. And I know it's picky but I really like decisions like taking bad things off from build time if possible, even if they are opt-in... Any ways, to me it's sad to see them closing the project, but I'm also hopeful some others as expert as they were on several of the topics they dealt with will fill up some of the the hole when they stop...