Password/logon data are stored in special cookies that the website stores on your computer.

Profile data can be removed or not recorded several ways;

• 1) Running Firefox in Private Mode (nothing is recorded)
• 2) Privacy settings; (In the address bar, type about:preferences#privacy<enter>)
• 3) Many disk cleaners and anti-virus type programs can remove data from browsers. Open their settings and have them leave the browsers alone.
• 4) Mal-ware.

You can use these steps to make a website recognize and remember you:

• You can create a cookie "Allow" exception to keep specific cookies, especially in case of secure websites and when cookies expire when Firefox is closed.
• Options/Preferences -> Privacy -> "Use custom settings for history" -> Cookies: Exceptions

Let the cookies expire when Firefox is closed to make them session cookies instead of using "Clear history when Firefox closes" to clear the cookies. .

• Firefox/Options/Preferences -> Privacy -> "Use custom settings for history" -> Cookies: Keep until: "I close Firefox"

You can create a cookie "Allow" exception to keep specific cookies.

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing cookies will remove all selected cookies including cookies with an "Allow" exception you may want to keep