My fault, my instructions were not very clear.
You need to configure the script (select it under Preferences / Toolbars / Scripts the click Configure), then double-click its ExtendedConfig line, and replace the two lines that relate to ftp://... in the default config with my ones:
"^ftp://SITE=(.*)\\?.*@.*//",
"ftp://$1://",
"^ftp://(.*)%20(.*)$",
"ftp://$1 $2",
"^ftp://(.*)%20(.*)$",
"ftp://$1 $2",
Here's what it should look like when done:
Then click OK in the three open windows (Edit Value, Edit Configuration, and Preferences itself) and it should take effect the next time a tab changes folder.