Note that it not considered good practice (polite) to make multiple connections to a server to speed up downloads as this usually happens when the server has limited capacity and can't offer more speed. By making more connections you may block other users from connecting to the server and downloading content.

If you want to do this anyway then you will need to look for an external download manager.

This download manager works separately from the browser. The browser tells it what to download, and off it goes.

http://www.freedownloadmanager.org It is a powerful modern download accelerator and organizer for Windows and Mac.

FredMcD said

http://www.freedownloadmanager.org It is a powerful modern download accelerator and organizer for Windows and Mac.

Hmm, I was using FDM under Windows for ages and didn't know it has a version for Mac - cool. Tho, for the out-of-browser solution and bigger files I'm using aria2c+aria-webui, but it's quite cumbersome. I was testing turbo-download-manager for in-browser solution but it still something extra.

Bottomline, I was hoping for something simple - i.e. possibility to simply tweak build-in DL manager to use more threads, but that's gonna happen as it seems...