Well, I used to use Gozilla a lot. But you're talking probably 12 or 13 years ago, when I still had dialup. Now, apparently I get 160 Mbps download, so everything I need or want I have within, like, 20 seconds. But maybe Gozilla still exists. You could try that. Or... doesn't the Firefox downloader have a pause function? This is quite the conundrum. I haven't experienced this in a long time. I know that some torrent programs will auto-close after DL and maybe even shut down your PC but I suppose that depends on if the mods you want are available as torrents or only as direct downloads.
Gozilla might still be around, you could check into that.