The post lists a number of ad-tech moves Mozilla has made in recent years, the ever increasing upper management salaries, and the insistence on trying to make Firefox preprocess everything you see on the web instead of showing you the web itself (AI).
I personally agree with these complaints. I think most people who intentionaly install Firefox agree with them. Despite all it's attempts otherwise, Firefox was and still is mostly used by "power users" and we're pretty much the only ones left that intentionally install the browser. Mozilla being the only working alternative to Alphabet domainance over the web doesn't change the validity of these issues. The real issue here is that Mozilla wants to be HUGE instead of just being a browser for humans.
I'd been a Firefox user since K-meleon (with a gap decade when Opera was actually a real browser and innovating). But for me the breaking point wasn't all this ad-tech stuff or the signalling of AI. It was when Mozilla showed they no longer cared about their core userbase and wanted to chase after demographics that didn't care about browsers at all; when they made the security theater Add-ons signing portal in version 37 and made it so one could not edit or install such things without Mozilla's central and continued approval (also, baking in 3 year expiring add-on certs making FF trial-ware). These days, for me, it's just a fallback for my bank. I use a Firefox fork for my main browsers which is much more Firefox than Firefox.