Large file downloads aren't easily manageable from any of the browsers on a Mac, but if you're looking for a little more control and a speed boost, SpeedTao does the trick.
The first time you run SpeedTao, you're asked to install extensions in all your browsers. This will trigger SpeedTao automatically when you download a file, but you can opt out and add only larger files if you like. To manually load files, all you need to do is drop a direct download link into SpeedTao. From here, you can set speed limits, or pause and resume. It's also a bit speedy than a browser's default downloader because it breaks the file into smaller chunks. Downloading the Ubuntu ISO took me about 13 minutes with SpeedTao and 18 minutes with Chrome. It's a free download from the SpeedTao website below.