The open-source company said Wednesday that the browser's 8,002,530 downloads in its first 24 hours of release set a Guinness World Record for the most software downloads in that period of time.
Mozilla Vice President of Marketing Paul Kim thanked Firefox fans in a statement, calling them "instrumental in achieving this record."
"Our community members came together and not only spread the word, but also took the initiative to help mobilize millions of people to demonstrate their belief that Firefox gives people the best possible online experience," he said.
Mozilla unveiled a campaign on May 28 to set the record, which previously did not exist.
The company asked Firefox enthusiasts to pledge to download the browser on the day it was released -- June 17, which it dubbed "Download Day."
Mozilla also hosted a Download Day event, the Camp Firefox BBQ, at its offices in Mountain View, California, and asked other Firefox fans to host similar download parties. It also encouraged people to place "Download Day" buttons on their Web sites as reminders of the big day.
Despite its eventual success, Firefox 3 Download Day didn't go off without a hitch. Interest in the endeavor crippled Mozilla's servers on the day of the release, so the U.S. part of the download process started about two hours later than originally planned when Mozilla's site wouldn't work properly.
The European leg of the effort began a little more than an hour later than planned and marked the start of the download-logging process. There were no more problems reported once the U.S. site was back up and running.