The company kicked off the effort at 10am Pacific time on Tuesday, officially releasing Firefox 3 to the public and starting the clock on the 24-hour race to a Guinness World Record for the most number of downloads in a single day.
Within an hour of the launch, however, a huge load of user traffic was threatening to sink the effort. Mozilla said that, at its peak, traffic for the new browser hit 14,000 downloads a minute.
Users were demanding a titanic 2Gbps in HTTP traffic alone, while download traffic hit 13Gbps.
By 12.30pm Pacific time, the unprecedented rush caused a download speeds to slow to a trickle.
At vnunet.com's offices in San Francisco, a download of Firefox 3 was slowed to around 5Kbps on an ADSL connection, far below average connection rates and slower than most dial-up connections.
While Mozilla's main site and the getfirefox.com domain were up, the spreadfirefox.com promotional site for the event remained down. By 2.00pm, the site was back online but traffic had slowed again.
Paul Kim, vice president of product marketing at Mozilla, said in a statement provided to vnunet.com that the company was currently serving around 8,000 downloads per minute.
Kim estimated that anywhere from five to seven million downloads would be served by the end of the first day.
"We are thrilled with the response to the release of Firefox 3," he said. " Our systems were busy earlier this morning so individual requests may not have got through, but they are all up now and serving a tremendous amount of traffic and downloads."
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