Considering that the adverb slowly is frequently replaced by slow, I find it curious that the adverb fast, meaning “quickly, rapidly,” seems to be acquiring an -ly ending.
Here are a few of thousands of examples of the incorrect usage to be found on the web:
What can i do to make my hair longer, but fastly
How do you play a tin whistle fastly?
How to earn fastly with google
I feel that time is moving fastly
As of 2011, “fastly” is non-standard English.
The correct form is fast:
What can I do to make my hair longer, fast?
How do you play a tin whistle fast?
How to earn fast with Google
I feel that time is moving fast.
Both slowly and slow are acceptable usage, but the contrasting word for them in standard English is fast.