Find the mistake: Being almost unknown ten years ago, these firms are now famous for its high-quality products and services.
Knowledge: Possessive adjectives
Its: its => show possessiveness for singular nouns, indicating things
Their: theirs, theirs => show possession for plural nouns
“these firms” is a plural noun.
Edit: its => their
Almost unknown ten years ago, these companies are now famous for their high quality products and services.