Your profile information is in a folder in your computers user folder. Also, the password files are encrypted.

If you want heavier encryption, see; https://support.mozilla.org/en-US/kb/use-master-password-protect-stored-logins Use a Master Password to protect stored logins and passwords

I want to change browser operation. In any web site after login by user, username and password save in my file and read other time for fill text box

I did not understand your last post.

step 1: (user open login web page) 1- User write username and password inside input elements 2- User click (login, enter, sign in , ...) submit button 3- Browser (Firefox) save user/pass in logins.JSON file that is encrypted 4- finish

step 2: other time (user open login web page) 1- Browser by URL fetch user/pass from logins.JSON also decrypt them 2- User click in username textbox so saved user/pass for this URL is shown 3- User by select one of them fill password textbox 4- finish

OK my friend?

Now in step 1 I want to change item 3 to: 1- User write username and password inside input elements 2- User click (login, enter, sign in , ...) submit button 3- My extension save user/pass in pass.txt file 4- finish

And step 2: 1- My extension by URL fetch user/pass from pass.txt 2- User click in username textbox so saved user/pass for this URL is shown 3- User by select one of them fill password textbox 4- finish

TNKS

Are you saying you want an extension to handle your passwords and not the Password Manager in Firefox?

Type about:preferences#security<enter> in the address bar. Look under Logins,

Note: For Firefox 56+ its; about:preferences#privacy Look under Forms & Passwords +++++++++++++++++++++++++++++++ Turn off Remember Logins. To check the passwords you have listed, press Saved Logins.