One thing that they've long waged a war on is browser add-ons (and, to a lesser extent, browser plug-ins); it's hard to imagine someone being more underhandedly hostile to these than Mozilla, short of not creating an extension framework in the first place (but that would only be hostile, not underhanded). Hanlon's Razor of course applies — but just barely.
In fact Mozilla has been waging a war of attrition against useful features in the browser in general; the usual reply to feature requests from users seems to be "create an extension for it", even when every single new "major" Firefox release (and there's a LOT of them) breaks extension compatibility.
What WILL stick a fork in the whole thing is the current plans to basically abandon extensions entirely now in late 2017, by removing the old extension framework (that everyone's using) and requiring extensions to be rewritten to use a new one (that basically noone's using). Mozilla has been hatching these plans since 2015, apparently, and is hell-bent on sticking to them.
Firefox in its default state is only semi-useful as a browser. I use a fair number of extensions — a couple have fallen by the wayside over time due to the aforementioned attrition, due to authors' inability and (understandable, frankly) unwillingness to keep on chasing ever-elusive APIs that change for nothing but the sake of change. Right now, almost 2 years after the announcement of the plans to abandon the old extension API, and with about 3 months left until it will be gone for good, there are 2 extensions (among the ones I use) that have been updated to use the new API, and 49 that have not.
2, vs. 49.
I don't foresee everyone suddenly scrambling to update extensions that haven't seen (or needed!) feature development in years, just to satisfy Mozilla's whims. Granted, stranger things have happened, but I'm not holding my breath, and if and when Firefox inevitably comes crashing down in flames this winter, I'll have to think long and hard about whether I can keep on using it.
And the only question THAT will depend on, really, is whether there'll be an alternative.
Is there? I'm not sure, frankly. All the cool kids long since moved on to Chrome, of course (and may well have moved on to something different again by now), but I don't want to use Google products ALL around. Opera is a decent effort, and I've been using it as an alternate browser since the days when you actually had to BUY it (unthinkable today, buying a browser, isn't it?), but it's just as inadequate as Firefox in its default state, and it never attracted much in the way of extension development. And what else is there, even?
I had high hopes for Firefox back in the day – I remember chipping in to pay for the two-page Firefox 1.0 in the New York Times, and being quite happy and proud that Netscape was being resurrected as what I hoped would turn out to be a lean, mean, user-oriented browser –, but it's all just gone downhill from there, and for many years Mozilla has veered between failed attempts to clone what they perceived as "closed" product (e.g. Android), inevitably wasting a lot of developer resources that way, and alternately pontificating about political and social causes that have absolutely zilch to do with its supposed mission of bringing a secure, open, user-oriented browser to the masses, one that's not beholden to the interests of large corporations with their own ulterior goals.
Firefox could have been so much, but these days it's a shadow of its former self. The blame for that squarely rests on Mozilla, and the moment I find a better alternative I'll have no qualms about abandoning it.