What to run
Open Remove Duplicate Lines. It stays in the browser.
How to read the result
First occurrence is kept.
Later copies are dropped.
Comparison is the whole line; a and a with a trailing space differ.
Order of first seen is preserved.
What to open next
Open Email Validator on what remains if they are addresses. It checks syntax only and stays in the browser.
Open Sort Lines if you also want A to Z. It stays in the browser.