Only someone with access to your computer user profile can see this.

^quote: Only someone with access to your computer user profile can see this.

That is not true. Without a master password you only would have to place a copy of logins.json and key3.db and place these files in a profile folder to see all passwords in the Password Manager. Only a MP can protect you against unauthorized access to the user names and passwords, so you should reconsider using a MP if you are uncomfortable. Note that the user names and passwords stored in logins.json are always encrypted with a basic key stored in key3,.kb and without the correct version of key3.db no access is possible.

Firefox 44+ will show the passwords column by default (Show Passwords is gone for now), but the passwords are initially obfuscated (bullets) and require a double-click to have the password visible. This new design is still under development, so it isn't sure how this will work once Firefox 44 gets released.