Below was pretty confusing. When setting open to a string I would expect it to be check relative vs absolute.

hostname: '0.0.0.0'
open: true
Opens browser with 0.0.0.0:8080

hostname: '0.0.0.0'
open: 'http://127.0.0.1:8080',
Opens browser with 0.0.0.0:8080/http://127.0.0.1:8080

hostname: 'localhost' (resolves to 127.0.0.1)
open: true
Errors with Warning: Could not start the PHP server: connect ECONNREFUSED 127.0.0.1:9119 Use --force to continue.
Likely would of opened 127.0.0.1:9119:8080 instead of localhost:8080