• Press the F10 key or tap the Alt key to bring up the "Menu Bar" temporarily if the menu bar is hidden.
• Use "Firefox > Options" instead of "Tools > Options" if the menu bar is hidden.

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
3. Press the Delete key (on Mac: Shift+Delete) to remove it.

You can remove saved Password(s) here:

• Firefox/Tools > Options > Security: Passwords: "Saved Passwords" > "Show Passwords"

• https://support.mozilla.org/kb/make-firefox-remember-usernames-and-passwords

How do I turn on my Remember passwords for sites: it is grayed out ?

Make sure that you do not run Firefox in (permanent) Private Browsing mode.

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy: Use custom settings for history
• Deselect: [ ] "Always use private browsing mode"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Instead of Tools > Options use:

• Mac: Firefox > Preferences
• Linux: Edit > Preferences
• Windows: Firefox > Options

Press F10 if the menu bar is hidden on Windows and Linux or use "Firefox > Options/Preferences"

Thanks it was driving me nuts, I do not remember ticking Private Browsing mode.