Meh, semantic discord.
First of all, -able is primarily denoting something able or fit to be done; second of all, "to second" is to agree with or support, and "secondable" is the ability or fitness to be seconded.
(1a) I second that suggestion.
(1b) That suggestion is secondable.
"First" doesn't exist as a verb as far as I know, but following the semantics of "second", it could be used to mean to initiate or do something for the first time, or to bring something to the front or otherwise a first ore foremost position. Thus "firstable" would be something able or fit to be initiated, suggested, set out, etc., or something able or fit to be placed before something else.
(2a) I want to first an idea for a book. (do for the first time)
(2b) That idea for a book is firstable.
(2a) I will first that article. (placing before others)
(2b) That article is firstable.
Count me out.
EDIT:
Besides, there are already shorter alternatives to "first of all", and "second of all": firstly, secondly; and there's no discord in these words. Bloody hippies...
