Well firstly that is wrong as a) http shouldn't be used for ftp e.g. ftp ://ftp (I have thrown in a space so it doesn't become a false link with the forum software, as yours did) and b) if this is truly an ftp download (which I doubt) then avast shouldn't scan ftp traffic. So something is wrong there.
That bit aside, your mask is incorrect, http :// ftp .mozilla.org/*.zip (excluding spaces) would exclude .zip files being downloaded from ftp.mozilla.org if you put *.mozilla.org/*.zip you wouldn't have to put any http, etc. in front.
*.mozilla.org/* would exclude all http port 80 traffic from mozilla.org, personally that is leaving a huge hole in your security. I trust mozilla but not that much.