Hi! Which OS do you use? On a Mac, you can find Mozilla settings in the Menu bar instead of using the appropriate icon on the browser window. Provide please the screenshot of your window.

See:

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins
• https://support.mozilla.org/en-US/kb/firefox-options-preferences-and-settings

There's a button at the extreme right of the toolbar containing the address bar consisting of 3 horizontal lines. Press that and select Passwords from the menu which appears. Otherwise you can enter about:logins in the address bar.