I was reading the Mozilla Doc about Firefox Addon Storage and it says:
Storage is a SQLite database API. It is available to trusted callers, meaning extensions and Firefox components only.
Well, it says its available to firefox only, but I managed to acess my Echofon storage by using a simple SQLite Manager for Linux. I found the .sqlite at:
/home/user/.mozilla/firefox/pmk9mj59.default/twitterfox_1.9.sqlite
The question is: how to protect my .sqlite storage in order to have it safe from external resources.
Anything on your local computer can access files with the right permissions on your local computer. The Mozilla document is talking about stuff running inside the browser (e.g. web content cannot access the database).