And the new features being added to Firefox of course are no reason to keep updating it.
For me, no, the new features are not compelling (and I wish many of them would cease to exist).
This is one of my main issues with the rapid-release stuff, that it's impossible to get bug fixes without getting unwanted new features.
Technology always moves forward. Should we pause all advancements to ensure that everything stays compatible?
No, but on the other hand, advancements come with a cost. Depending on the user's needs, it can be that the cost isn't worth it to them. In the case of FF, the cost is nowhere near worth it for me. I cannot even imagine a new browser feature that would be so compelling that I'm willing to sacrifice compatibility for it, although that's probably due to my own lack of imagination.
And why is it that this library (not sure what to call it) is the one with the problems? If firefox updates are breaking it, then something must be broken with the library itself.
As I commented above, for me this isn't about blame. This is about the usefulness of the tool, and FF is becoming less useful (for me) over time. Whether this is the fault of FF or not is irrelevant. If FF can't do what I need, for any reason, then it can't do what I need.