Passwords cleared with Clear Private Data
Firefox's Clear Private Data feature might be set to clear your passwords when you close Firefox.
1. At the top of the Firefox windowOn the menu bar, click on the ToolsFirefoxEdit menu, and select Options...Preferences....
2. Select the Privacy panel.
3. If Always clear my private data when I close Firefox is not selected, your Firefox is not set to clear your passwords when you close it. You can skip to the next section.
4. If Always clear my private data when I close Firefox is selected, click on the Settings... button.
5. Make sure that Saved Passwords is not check marked.
6. Click OK.
7. Click OKClose the preferences window. Firefox is now configured to not clear your passwords when closing.
Cannot use or save passwords after upgrading Firefox
If you have passwords that contain non-ASCII characters, there is a bug in Firefox 3.0.2 preventing Firefox from remembering passwords. For more information see Cannot use or save passwords after upgrading Firefox.
This might help.