Jama is correct Friendly is an adjective but quickly is an adverb. This is why they follow different rules. The adjective is quick (quick, quicker, the quickest). However, the rules for comparatives are very fluid. You will often hear: He speaks quickly. She speaks quicker. I speak the quickest - not the standard way to compare adverbs but not uncommon. You will also hear: She is much more friendly than her sister - not the standard way to compare adjectives which end in 'ly'. The rules are not as fixed as English lessons often suggest :)

Also, just as an aside, people will more often say “quicker” not “more quickly” (in North American English, at least) : )

English has many patterns that are not consistent. I think that the reason is because it's a blend of different languages. Latin, Greek and some French and German too.

“Friendly” is an adjective while “quickly” is an adverb. Perhaps that is why.

Don’t forget: Quickly- quicker- quickest Quickly- ly- did something a certain way- fast Quicker- one thing is more quick/fast than another thing- comparative Quickest- of all options this is the fastest- the best, the optimal