Most web browsers have a feature that remembers information you type into forms on the web. This is often a convenience, saving time when you fill in a lot of forms. But it's also a little risky because the browser might remember private info you type into forms, such as your credit card number, passwords, medical conditions, date of birth, etc. Disabling these "auto-fill" features is usually pretty simple in the "Options" "Preferences" or "Settings" panels of your browser.
Here's how it looks in Firefox