Presuming you accidentality saved your login password and you do not want your information from being unintentionally saved or used in your browser. Please follow these steps to disable and clear it.

In Google Chrome, you can turn off autofill data, and delete the data before.

Click the Chrome menu icon (In the top right of the browser) then click on the Settings menu.

In the "Autofill" section, expand the area for which you wish to disable Autofill. (In this scenario i choose Password).

Turn it off and the settings will save the changes.

Press CTRL+SHIFT+DEL on your keyboard then go to the "Advanced" tab.

At the top, choose “All Time” option to erase the autofill from the very beginning.

Make sure that the “Autofill Form Data” is checked, and click "Clear Data." to continue the process.

In Firefox, you can turn off autofill data, and delete the data you have inputted before.

Click on the Firefox menu icon. (In the top right of the browser), then click on settings. Select "Privacy & Security.", and scroll down until Logins and Passwords section.

In the "Logins and Passwords" section. uncheck "Autofill logins and passwords." The system will automatically save your settings.

Press CTRL+SHIFT+DEL, In the "Time Range to Clear" dropdown menu, select “Everything.” to erase the autofill from the very beginning.

Make sure “Form & Search History” option is checked, then click OK to continue.

Notes :

Delete autofill in Firefox may also delete your browsing history.