As Firefox (32-bit) was getting unresponsive, presumably due to maxing out its process RAM, I've just installed an official 64-bit version of Firefox from this page because i'm a developer and according to this page it's
The only browser made just for developers, Firefox Developer Edition was created with your workflow in mind. Build, test, scale and more all from one place, for the first time ever.
That lacks the option to import from my old Firefox profile, though. I've imported my Chrome stuff, but still wonder whether there's an equally simple way to get my old Firefox profile cookies and passwords into this fresh install.