A very promising application... 1Passwd. It allows Firefox's passwords be stored in a central location - Keychain Access, and be shared with other application such as our beloved Safari.
Why bother storing same password sets repetitively in different browsers?
Keychain Access is a system-wide secure password manager that most Mac OS X applications can use to store logins for things like websites and FTP access.
And if you have .Mac account, it will be synced as well.
1Passwd also comes with Firefox Extensions, save form and fill form.
1Passwd is currently available in beta, it's a bit expensive... US$29.95 per license.
Download 1Passwd now! (free functional version available)