first of all vs foremost

first of all is not an adjective while foremost is an adjective.

Word	Noun	Adjective	Verb	Adverb
first of all	No	No	No	Yes
foremost	No	Yes	No	Yes

As adverbs, first of all and foremost are synonyms defined as:

Other synonyms of first of all include first, first off, firstly.

first of all (adjective)	foremost (adjective)
	ranking above all others
	situated closest to the bow
	preceding all others in spatial position

first of all (adverb)	foremost (adverb)
before anything else	prominently forward
	before anything else