If you are using Firefox3 there is an addon called Foxmarks which stores both bookmarks and passwords online, enabling easy synchronising between computers (even of differing OSs) which may be of interest.

I don't regard my bookmarks as a security risk, and just use that feature, which also works for earlier Firefox incarnations. It does the job well.

I might use the password function if I was logging into lots of chat sites and such, but I don't do that, and wouldn't trust the security of an online storage with any important passwords.

I expect that Firefox has a file for all the passwords, but I can't offer any guidance, maybe one of our resident gurus will show up soon.