Is Firefox slowly dying and why?

[Anux]

I just installed a firefox with a new profile to do some tests in a VM and got really frustrated in the process (spending about half an hour customizing it to be usable). Im a fellow user since atleast 15 years and loved that thing for the first 10 or so and got more and more anoyed by it in the last few years.

If you look at any statistic in the interwebs they might differ slightly in numbers but all show a steady decline of firefox: https://gs.statcounter.com/browser-m...-202007-202307

I have a few theories why that is and want to vent my frustration here a bit and maybe see a different view from others:

1. Chromes agressive marketing

   This was atleast a big contributor in Chromes early days, many people switched because their search engine and webmail told them they needed to.
   On the other hand most users get used to specific software and are hard to convince to use alternatives even if they are better, they really need to be unhappy with the software to change.
   One argument I hear a lot "firefox was/is extremly slow" but I used it all the time with old, slow hardware and never had the feeling it was to slow. Maybe specific bugs, websites or plugins? Was facebook slow in FF?

2. The chase for Chromes userbase / abondoning or ignoring their strongest users

   I think since Firefox started it's 2 week release cycle they also tryed to become the next Chrome to win those users back. Problem is by chasing the market leader you will always be behind it and why would a chrome user use a chrome that lags behind?
   In that process firefox abondoned their core userbase: geeks, freaks, nerds, devs, it-admins, ... they used it mostly for it's amazing flexibility, it had the most addons by far and it's UI was highly configurable at the time. Sure this usergroup seems small but it's those guys that bring many standard users with them (admin at large company, dev developing plugins, ...).
   I atleast feel like loosing a customization option every 2 weeks.

3. Mozilla lead beeing corrupt

   I was once a donor, not much for sure, but steady. Stopped after I recognized what they shove up their CEOs ass. I imagine many others think the same and if they joined recently they won't even start spending.
   I will only ever start spending again if the CEOs get the same money as the devs and maybe a bonus if marketshare increases.

4. Constant and forced changes to UI

   That's what buggers me the most in the recent days, I could even ignore it if they wouldn't make the really bad things non optional. Just why? It's like they try to push away even the donkeys that don't want to leave.

5. 1000 new features that should always just have been optional extensions

   Pocket, VPN, extension puzzle icon, and countless other things. All that I can I turn of per UI or about:config so I forget about the most but with every release there is atleast one new "feature" that gets shoved in your face.
   It's okay to develop this stuff and make advertisment for it on new releases but why force push it?

So far my theories, am I wrong? The decline is undenyable but maybe I have a distorted view on the reasons.

I'm in the process of testing alternatives, anyone know a fork that has:
firefox engine but with custom and fully customizable UI
100% addon compatible
fast security updates but the rest of the developement is preferably slow and conservative
basically nothing of the stuff I criticised above

I don't like Chrome based browsers (just a subjective thing) and I would rather not discuss Chrome in this thread or have a browser flamewar.