Stored password in Safari Versus Firefox
Safari stores its passwords in the OSX Keychain.  Open /Applications/Utilities/Keychain Access.app, select the "Login" keychain (this should be default) and select "Passwords" under "Category".  Doubleclick an entry and check "Show password"; you'll be asked for your login keychain password (this is usually the same as your account password).

(For a while I was using an add-on for Firefox that used the Keychain, but it was highly broken.)