So it might seem to you that no power user could possibly be totally happy, I am happy to prove you wrong.
The problem is that Firefox makes these promises and builds a platform (in this case, old-school XUL-powered extensions), builds a profitable user-base from said platform, and then yanks features at a whim. It is almost like a classic bait-and-switch but played in slow motion. In the case of Firefox there simply aren't suitable replacements available for many add-ons because the APIs and underlying features they relied on are being pulled. And they are being pulled because of managerial decisions, made to metrics that only highlight majority use-cases, in the name of "saving programmer bandwidth". As a result, a popular, powerful, useful program more and becomes more like a disposable appliance and less like an extension of the mind.
"Who cares about nice ideals like mind extensions blah blah blah" you think? Well, a lot of users do (especially us old nerds), many of us who have stuck by Mozilla and will willingly dance to their beat in exchange for the company's historical sense of economy in its asks and respect for its userbase.
If Mozilla were making Firefox out of the kindness of their hearts, maybe you would have an argument. But Mozilla is a million-dollar business and much of what has become of their flagship browser lately is a result of business decisions to bring in more money, so I have a hard time understanding how legitimate user complaints could be considered "entitled".
Increasingly, that means having a Web browser that is secure and fast, even at the expense of taking out features that some users really wanted. I've been using Firefox since the start (you can find my name on the famous NYT advert), and they have not removed a single feature that I care about.
On the contrary, I am now happier with Firefox that I have been for many years.
It really makes me sick. Tyranny of the majority writ large. (And while I write this from within Firefox, I am definitely not a very happy user of it any more.)
You're right about Mozilla's nonprofit status -- but it is easy to forget about with all the various business partnerships they seem to enter. It makes me wonder just how much of this nonprofit is really spent funding development/advocacy...
Firefox is fast, modern, feature rich, and, free browser. Your grievance is about missing some feature that you use.
The right analogy would be that the church is providing perfectly nutritious food that majority of the people eat, but a homeless guy is griping about not having wine with the meal. After all the homeless guy is old now and he is used to having wine with meals.