NEW YORK (AP) — In just five hours, the new version of the Firefox Web browser had as many downloads as its predecessor got during its entire first day, the software's developers say.

Firefox 3 reached 1.6 million downloads by early evening Tuesday to match Firefox 2's first-day downloads. In the opening hours, Firefox's Web site was distributing nearly 9,000 copies of the free software every minute.

Downloads continued Wednesday as Firefox supporters sought to set a world record for most software downloads in a 24-hour period. The category is new, and Guinness World Records must certify it, a process that could take a week or longer.

Tuesday's release was delayed as visitors checking for the update overloaded Firefox's Web servers. The site was slow or unreachable for about two hours starting about 12:45 p.m. Eastern time, 15 minutes before the scheduled release time, according to AlertSite, an Internet performance monitoring company. Performance improved later in the day.

Firefox comes from Mozilla, an open-source community in which thousands of people, mostly volunteers, collectively develop free products. Firefox is the No. 2 Web browser behind Microsoft Corp.'s Internet Explorer.

Firefox 3 includes enhancements to help users organize their frequently visited Web sites and block access to sites known to distribute viruses and other malicious software.

Users of Yahoo Inc.'s mail service can also use Firefox 3 to send e-mail by clicking a "mailto" link they might come across clicking on a name or a "contact us" link on a Web page. Previously such links could only open a standalone, desktop e-mail program.

Firefox 3 also offers other design and speed improvements.