Did you try to "refresh"? See https://news.ycombinator.com/item?id=13227658
Despite this, I've completely wiped out both my settings and firefox install on several occasions in an attempt to keep things stable.
It doesn't help.
I'm aware that my addons are likely a big contributor to the memory-hogging and eventual crashes, but if I didn't want to use these addons, I'd just use fucking chrome. The ENTIRE point of Firefox is for the customizability. Dropping addons to improve stability just isn't an option for me.
I'll keep an eye on it to see if there's a specific addon triggering my issues, but it will likely stick around.