Firstness is the mode or element of being by which any subject is such as it is, positively and regardless of everything else; or rather, the category is not bound down to this particular conception but is the element which is characteristic and peculiar in this definition and is a prominent ingredient in the ideas of quality, qualitativeness, absoluteness, originality, variety, chance, possibility, form, essence, feeling, etc.
This quote has been taken from Kenneth Laine Ketner's 1983 reconstruction of Peirce's 'Autobiography'
http://www.commens.org/dictionary/entry/quote-brief-intellectual-autobiography-charles-sanders-peirce-15