Try copy-pasting a link that has actual whitespace in its URL queries and see if it gets linkified correctly. Just because you can doesn't mean you should! A space is like the one delimiter that is applicable for separating out URLs from the context of a larger blob of text.
You are right. Seems firefox displays %20 as whitespace and converts whitespace to %20 when you use it. Chrome displays it as %20 but still converts whitespace to %20 if you try to use it.
