https://support.mozilla.org/en-US/kb/password-manager-remember-delete-change-and-import
You can easily manage the usernames and passwords that Firefox has saved for you.
- Click the menu button
and choose Options.
- Click the Privacy & Security panel.
- Click Saved Logins… under Forms & Passwords. The Password Manager will open.
- To see the passwords you have saved, click Show Passwords. When you close the window, your passwords will be automatically hidden.
- Use the search box to find a particular website or username. Click the X in the search bar to clear your search and see the full list again.
- To remove the username and password for a website, select the site's entry from the list and click Remove.
- To remove all stored usernames and passwords, click Remove All. After confirming this choice, all of your stored usernames and passwords will be deleted.
- To import passwords from Chrome or Internet Explorer, click Import… and follow the instructions in the wizard.