After my recent post about Firefox Annoyances: Download Resume Problems I observed that some of my readers were trying to find out how to resume their half-downloaded files in firefox/iceweasel. Sorry, the Firefox / Iceweasel doesn't yet continue half-downloaded between network failure or crashes. However you can try this alternative method.
Here is how you can continue the download from a crashed firefox / iceweasel using wget. First lets get rid of '.part' extension that the browser adds while downloading.
mv BigFile.zip.part BigFile.zip
Now resume/continue the download with wget's "-c / --continue" option.
wget --continue http://www.SomeSite.com/files/BigFile.zip