Well, like Tech, I'm not very paranoid about all of this.
But, on the other hand, I'm not stupid either. None of my banking account passwords, or any others that access sensitive information, are stored, and they are super strong.
I've never looked into third party password managers as David alludes to, but, in my case, the only passwords that are saved in Firefox, are accesses to sites like this one. If any one "captures" those, I frankly couldn't care less. I would just change them.
Being Linux only, the chances of anything like this happening, is pretty slim anyway. They'd have to crack me with a kit, and I run a detector regularly, and if anything showed up, I wouldn't hesitate to reinstall in literally the next heartbeat. Tech would do the same thing.