Click in the field, enter a character or two and STOP ! Using the arrow keys, highlight an unwanted entry. Then press Shift > Delete

Repeat as needed.

That does not work.

What kind of form data is this ? Is this normal saved form data or login data (have a key icon in front in the drop down list) or possibly address or credit card data ?

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins

The page in question is a login page on t-mobile.com. When I put the cursor in the box it initially fills some data - this is what I want to delete. After a moment the LastPass add-in takes over and offers to fill username etc. That is why the simple method (as FredMcD described) to delete this data does not work.

Disable the Password Manager and try again.

What login data do you want to remove ? Is that only the Firefox login data ?

You should be able to remove this login in Lockwise (about:logins).

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins