First, I actually do respect your views and I'm pleased you've had the fortitude to responded as such.
To respond adequately to your post would require me to start detailing what I (and many others) reckon what's wrong with Firefox (and similarly so with Thunderbird). Clearly that's not very practical here, as to do so we'd be bogged down in detail and the key points of the argument would be lost.
That said and not wanting to let anyone assume I'm avoiding your points, I've divided an overview of the key objections into the following groups.
1. Features that by their intrinsic nature should be in both Firefox and Thunderbird but which are missing. These are left to be picked by add-on developers who eventually give up after Mozilla breaks the compatibility model once too often. Thus a useful feature we'd gotten used to via an add-on literally disappears with an upgrade (more about this in point 2.)
2. The single biggest fiasco with Firefox from a user's perspective is Mozilla's perennial breaking of its add-ons. Not only is this disrespectful to third-party developers who develop them, and it often turns them off from doing further development work, but also it infuriates users whenever their add-ons no longer work.
In essence, when an add-on no longer works after an upgrade, users consider such an upgrade as actually a downgrade in terms of performance and user ergonomics. Whilst Mozilla may have done this for noble reasons such as improved security it's of very little concern or comfort to the average user (myself included) whose facility no longer works. As far as he/she is concerned, Mozilla has fucked up yet again - and I'm not exaggerating here, it's been a constant theme for Mozilla to blatantly ignore compatibility from the early 2000s until today. Just go to Mozilla's add-ons site and check the huge number of incompatibility issues one finds even with the items that are still listed (many are not).
For the record, I'll mention just one add-on that should have been in the core program that was fixed by an add-on which was later busted by a 'retrograde' Mozilla 'upgrade' and that was Lazarus, it very usefully allowed undos in dialogue boxes etc. which often get lost for nefarious reasons after one has typed much text. If just about every text editor and wordprocessor has multiple levels of undo then why doesn't Firefox?
[Edit, Firefox's not alone here, I just lost many edits whilst editing typos in this post from my mobile. Had undo worked then there'd had been no problem. Thus it's a problem with many browsers. No, I'm not using Firefox or Chrome here.]
As stated, whilst there may be many reasonable excuses for why Mozilla acted the way it did, the user isn't interested in hearing any of them - all he/she knows is that a useful feature that once worked now doesn't and Mozilla's actions are the reason. Many of us remember those failures and it's why so many of us go to inordinate lengths to nuke automatic updates, as they're likely to backfire just when we least expect it (inconviently in the middle of an important job etc.).
The picture that such actions (and there's been many of them) engender in many of us users is that Mozilla programers primarily program out of self-interest rather than that of users' actual needs. Naturally, you programmers prefer simpler, cleaner code that doesn't support legacy features - similarly, it seems none of you are prepared to do the extra yard work - the extra coding - need to keep old-API add-ons safe. I know, it's boring shit, and no one will do so willingly, they have to be compelled to do so, and no one in authority at Mozilla has made that call (and that alone speaks a great deal about the ethos/culture at Mozilla).
Again, just get it into your heads that no one other than you Mozilla programmers care a damn about the reasons why you nuked XUL/NPAPI as laudable as you at Mozilla deem their nuking to be. Morever, many of us aren't interested in DRM or pandering to the tech giants. Include new features if you must but at least provide us users with the option to let us turn them off.
As you've seen with Firefox, sticking to some moral highgound, or overdoing security above all else - not to mention overly pandering to new web standards forced on us by the new owners of the Internet, Google Facebook et all, has its heavy penalties. Provide these features by all means but stop taking full responsibility for a user's security. If he/she wants to deliberately downgrade his/her security from the default then so be it, you've no right or ultimate authority to dictate that. Moreover, if you want to pander to the security mob, then I'd again point to the fact that such righteousness has cost Mozilla dearly in market share.
For instance, the first of these forced annoyances was the removal of the switch to turn JavaScript off. Right, default it to 'on' for the majority who wish to use it but it's down outright authoritarian programming to insist that you programers know best - especially when you seemingly haven't a clue about user ergonomics or what actually annoys users (and I've a damned good idea having run an IT department for years only to find myself continually falling foul of users who blame me and or my staff as they hold us directly responsible for your 'irresponsible' programming changes).
Why you programers want to be on such a power kick is something that only psychologists can figure out if that's at all possible. Of course, it's not only Mozilla programmers here, Microsoft's are possibly the worst. It's the sheer arrogance that you programners display when you think you know what's best for users when you often don't have a clue which is so annoying (I'm not aiming specifically at Mozilla programmers here, rather that inflated ego is characteristic of breed). BTW, I've done a considerable amount of programming in my time but I don't consider myself a professional programer.
3. Similarly, instead of fixing boring bugs such as those longstanding ones in the printer routine and the overall outdatedness of the printer routine per se, not to mention that other first-class annoyance - the failure of text selected by the mouse to be copied from the context menu thus it requires a full highlight followed by CTRL-C then CTRL-V to actually work - you Mozilla programers simply ignore them year after year. Right, fixing bugs is boring, but adding new features obviosly isn't - even if many users deem them unnecessary or of secondary importance to rectifying problems with the more utilitarian features of the program. I mention Australis here. As it's clear it annoyed the hell out of many users, thus it's fitting to ask why Mozilla didn't include an optional fallback to the older UI. Right, I've already answered that point.
4. If Mozilla's programmers genuinely claim they're trying to do the right thing by users then it's almost impossible to conclude that they actually understand users - or what features users actually want from a browser. (Who do you ask and why doesn't Mozilla respond to the many thousands of complaints just like mine?) Yes, it's a restatement of what I've already said, but it has to be true or otherwise Firefox's usage ratings wouldn't be nosediving off the graph. An adjunct to that is that Mozilla never fully levels with its users concerning the real reasons for why its takes certain actions - that is other than to dress up changes with PR-speak and spin. If Mozilla's leveled with users more honesty then users would likely reciprocate. Moreover, you would have fewer users like me upping hyperbole to critical levels out of sheer frustration.
Finally, likewise, I don't understand why you can't see my reasoning for why the Firefox 94 webpage contains said info you mentioned. I'll get the quote and post it here when I've a moment.
Again, what I've said hurts and I know it. Please understand it's no vendetta and it hurts me to be so negative (especially when there's so much negativity about these days); and it also hurts to see the only essentially independent browser going down the gurgler when it ought not to be. You should spare a thought for people like me who insist that the corporate browser should be Firefox only to find us between a rock and a hard place when it all goes belly-up for the many reasons mentioned. Defending Firefox against Chrome is no easy task these days.