75% of the people who download Firefox don't become active users

According to the Mozilla wiki: "In order for Firefox to reach our market share goals, we need to improve our ability to retain users. Currently, approximately 50% of the people who download Firefox actually try it and about 50% of those people continue to use it actively."
Firefox's claims to success have been supported by clocking up the number of downloads, encouraged by payments from Google, but it turns out that 75% of the people making those downloads don't "continue to use it actively."