> but currently there are a few thousand about:config options, and the number seems to keep growing.
But those configurations are not very discoverable, not well documented, are in constant flux, and if you set them incorrectly can really mess up your browser (I speak from experience).
> I'll also mention that only one person needs to create the build, once you do that then anyone else can run that build
From my understanding, if I were to distribute my custom build I would also need to change all the firefox branding, since Mozilla has trademarks on it, which increases the effort even more.
I think the huge number of about:config options is actually a major problem for Firefox, there is no possible way to test all those options and ensure they stay working forever and have zero regressions. You won't like this, but a lot of them probably need to be removed.
You would need to change the branding but I think some of the other Firefox modifications have systems in place to deal with that. If you ever need to do it, maybe it would be worth asking them.
I'll also mention that only one person needs to create the build, once you do that then anyone else can run that build. That's usually how development works, and in fact this is already the gist of how Mozilla tests their unstable builds.
>the customisability is decreasing, more features are being removed than added
I can't agree with this, maybe the amount of visible settings in the preferences has been reduced, but currently there are a few thousand about:config options, and the number seems to keep growing.
>But they are also bleeding users, so something is clearly not working for them. And maybe, as the OP suggests it is because of changes that anger a minority of their users.
For many years I asked people why they were switching to Chrome and I got various answers, very few of them were because of something negative about another browser, and most of them were about what they liked about Chrome. That's just my personal anecdote. It also just seems to me that Mozilla is in a bad place where people say they drop Firefox because they like Chrome, so Mozilla switches gears to make it more like Chrome, and then people complain it's not unique enough anymore and it's missing some old non-Chrome feature. How could they possibly win here?