But I was having a problem: when I would download something, the browser started hanging for 10-15 seconds. This was annoying when I was trying to leech the Futari Ecchi manga pages; it took hours to complete 10 chapters, which was one tankobon. I figured, though, that it was just that web site.
Then, when I was trying to grab some torrents, I realized that no, it wasn't just the manga site--it was everything. Torrents usually took a second or two--at most!--and now it was 30 seconds from the time I clicked on the link to the time that I could do anything else in the browser window.
What I had not done was click the little "clean up" button in the lower-right corner of the download window. I had thought that button would delete the downloaded files, you see. But that's not what it does; it merely removes them from Firefox's ken. Once the files are downloaded and saved, Firefox no longer needs to know where they are; the download window keeps a list of links to every single file on it unless you clean up once in a while.
That's why it was so slow: however Firefox stores that information, it had become too cumbersome for the program to manage efficiently. This is why I had to wait while the browser un-hung itself; it was appending file data to a ridiculously huge database of useless information.
Now that it's cleared out, I'm back to quick downloading.