As someone who switches browsers about every six months, I feel that Firefox is still quite a bit behind in terms of stability and performance. I mostly blame the single-process model, which makes crashes and hangups way more global than they should be in 2014.
On Windows, there's also the 32-bit issue. On machines with 8+ GB of RAM, having all tabs share a 2 GB address space just doesn't cut it. Especially when your addon model, one of the key features that sets Firefox apart from other browsers, eats an additional 4 MB of this limited space per tab (and that's just for one addon).[1]
Having said all that, I know that brilliant people are working on fixing this, and there have been huge improvements in the past year. And that's how I hope they'll win back users: by building a better browser, not just by appealing to open-source ideals and fear.
[1] https://blog.mozilla.org/nnethercote/2014/05/14/adblock-plus...