This is one of google's things, not specific to firefox. You can fix it by creating different firefox profiles for the user. You can run the profile manager by performing the commands as follows:

Windows Vista/7

   Click the Start button
   Click the search bar at the bottom.
   Type "firefox -ProfileManager"

Windows 8/8.1

   Press "Windows + R" on your keyboard.
   Type "firefox -ProfileManager".

That will make a separate Firefox for every user, which will fix your problem if each person signs in to their Firefox profile.

Have a great day!!

Jon

Hello,

Try some of these:

• Control whether Firefox automatically fills in forms

At the bottom click on Sign in with a different account then Remove account

Use these steps to remove saved (form) data from a drop-down list:

1. click the (empty) input field on the web page to open the drop-down list
2. highlight an entry in the drop-down list with the mouse or cursor Down key
   do not click the mouse or press the Enter key
3. press the Delete key (on Mac: Shift+Delete) to delete the highlighted entry

agreee this works in the drop down but my problem is on the sign on page for Gmail were as all users email addresses show up in the sign in box. thanks for your input