The words firry, furry sound the same but have different meanings and spellings. Why do firry, furry sound the same even though they are completely different words?
The answer is simple: firry, furry are homophones of the English language.
Made of fir.
Abounding in firs.
Consisting of or similar to fur.
Covered with, wearing, or trimmed with fur.
Covered with a furlike substance.
Having a furlike quality, as in tone; fuzzy: a furry voice.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").