There was some malware going around last year that created a task in the Windows Task Scheduler to open a particular URL at the same time every day (an ad of some kind). To check for a scheduled task: Windows XP: Start button > [All] Programs > Accessories> System Tools > Scheduled Tasks Windows Vista/7: Start button > Control Panel > System and Security > Administrative Tools > Task Scheduler More resources: (1) Past threads on the "dsite" problem: https://support.mozilla.org/search?sortby=1&a=1&w=2&q=dsite (2) Suggested malware scanners: [[Troubleshoot Firefox issues caused by malware]]. Any luck getting rid of it?