To prevent this from happening, you can set a master password so that anyone using your account in Firefox can't just use your web site passwords without knowing it. Follow the instructions below to set a master password:
- Launch the Firefox browser.
- From the Tools menu, select Options...
- Click on the Privacy tab, and click on the Passwords sub-tab
- Press the 'Change Master Password' button.
- Enter a strong password (see the following article for creating a strong password)
- Press the OK button