Yes as the other two said, the Repl storage should not increase if you download the Repl to your computer. This downloads a copy of the Repl, and should count against your computer storage space (your hard drive), but not against your Repl.
I’m pretty sure they are talking about using Firefox within a Repl to download files.
I think one reason it wouldn’t add to the Repl’s storage counter is because it is downloading outside the /home/runner/[repl_slug] folder. Testing this within my own Repl confirms this, as it creates a Downloads folder (/home/runner/Downloads) with the files I downloaded in there. Using something like nautilus (or even the shell) to transfer files from this folder into the Repl’s designated folder seems to work correctly.
@a747 Yes, that is what I meant. When you download a file through the Repl, it goes into the Downloads directory, therefore not counting towards Storage Quota.