If you have to download a large file, but it isn't needed right away, use this lightweight Firefox addon for scheduling your download for a later time.
After installing the download scheduler extension, you will have a context-menu option to "Schedule Link As..." which will add the download to the scheduled time.
Options for your schedule are located in the Addons menu in Options for the Download Scheduler plugin. You can set a time for it to start and stop.
This simple addon is a must-have if you need to postpone your larger downloads for a later time. It works in Firefox 3.5 through 4.0.