You can add autocomplete entries to modifiers with a known list of names and/or values, allowing you to fill them in more quickly.
Click on
button on the right side of the Request headers or Response headers title, then select Customize autocomplete.
Fill in the Name and Value text area with one autocomplete entry per line.
Click Done once you are finish.
Now when you focus on the name or value textbox in ModHeader, the autocomplete value will show up.
Note: If you set autocomplete entries for Request headers, then those entries will only show up for Request headers textboxes, and not for other types of modifications.