How to read local storage of Mozilla?

From this question I found out that Mozilla saves local storage in webappsstore.sqlite file. From my own question I found out that this file can be found in this folder (at least in my case):

C:\\Users\\*\\AppData\\Roaming\\Mozilla\\Firefox\\Profiles\\*.default\\

Now I want to read the local storage. I try the following:

conn = sqlite3.connect('webappsstore.sqlite')
c = conn.cursor()
c.execute("select * from ItemTable")

As a result I get:

DatabaseError: file is encrypted or is not a database

So, I think it is encrypted (because from the extension I can conclude that it is a database). I also would like to note that the same approached worked well for Chromium.