Comment 114 for bug 357864

(In reply to Josiah Bruner from comment #109)
> It would also be preferable to allow clicking the drop down icon to always
> bring up the list, regardless of the field's current state.

It does on sane platforms, thus the original version always had the field editable.

Just to make sure that we're looking at the same thing here, there are other editable lists in the UI. The easiest one is the advanced attribute editor. Compose an HTML message, then go to Format - Page Colours and Background, then click Advanced Edit. On the bottom left is an editable list of commonly used attributes (background, bgcolor, text, link, vlink, alink, id, class, title, lang, dir).