largely vs mostly

largely and mostly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
largely	No	No	No	Yes
mostly	No	No	No	Yes

As adverbs, largely and mostly are synonyms defined as:

Other synonyms of largely include for the most part.

largely (adverb)	mostly (adverb)
in large part; mainly or chiefly	in large part; mainly or chiefly
on a large scale	usually; as a rule