I know for a fact that Mozilla leadership does prioritize crashes and resource usage (in fact, this is one reason for all of the work on the process separation feature called Electrolysis), but of course they will prioritize crashes that affect lots of users. For various reasons, it could be that your crashes are different from those. (I'll assume that you're on the most recent version of Firefox already.)
FF just has poor QA. That's a problem and all the excuse making actually hurts the product as FF leadership isn't seeing enough complaints apparantly, when an army of nerds are refusing to acknowledged these problems.
Extensions are commonly blamed because of the way that Firefox implements extensions.
They essentially become a fully integrated part of the browser with full privileges. When extensions do things that they shouldn't be doing (but can anyway, because what's stopping them?), the extensions are blamed.
Of course there have been many lessons learned from a decade-old extension ecosystem. Other, newer browsers have benefitted from those lessons (ie. Chrome). Mozillians know the problems with the current extension model but the hard part is having the resources to do something about it.
"Yet somehow Chrome/Chromium exists just fine without me writing big reports for it, same for Safari, IE, etc."
SOMEBODY is writing bug reports. FWIW, there are what, 50000 Google employees, a majority of which could be dogfooding prerelease Chrome and filing bugs. Mozilla has 1/50 of that to dogfood Firefox and depends heavily on its community to make contributions.