Sure there are tools, downloads and services that may do this for you, but what fun is that?  Just in case you don’t feel the need to download another addition to the browser just yet – here is how you can backup your Firefox saved passwords the manual way.
First, navigate yourself to your profiles folder and then you want to copy three files, they are named:

signons.txt
signons2.txt
key3.db

Copy and past them into the place you want to back them up to, and [...]