SKdownloader is a download accelerator that created from java, so it can be installed in windows and linux OS from any Java Virtual Machine (jre). The features almost the same as a resume idm download, proxy, schedule, torrent, split up to 10 parts, integration in firefox. I think this is the best because it does not use such complicated prozilla or axel.
Previously, there must be a java virtual machine (jre) version 1.6 and above, if no please download http://www.java.com/en/download/linux_manual.jsp
Download the file http://www.toolsbysk.com/skdownloader/downloads/linux/index.html
move to the directory usually /Download, if in linux
$ cd /Downloads
$ su (to root access) here
# sh. /skdownloader_linux_installer.sh
for extension firefox can download it http://www.toolsbysk.com/skdownloader/downloads/skdownloader.xpi