Firefox 5. You are using an outdated, obsolet, unsupported version of Firefox which is no longer maintain. Please upgrade your browser to Firefox 10 and check

• getfirefox.com

Make sure that you are using latest version of Downloadhelper Addon?

• downloadhelper.net

if this issue still occur, please also contact download helper support

It is possible that your anti-virus software is corrupting the downloaded files or otherwise interfering with downloading files by Firefox.
Try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.

See "Disable virus scanning in Firefox preferences - Windows"

• http://kb.mozillazine.org/Unable_to_save_or_download_files

See [/questions/761494]

• Move the old .part partial download and the final file without the .part that has size 0 to another location.
• Start a new download and pause it, don't close Firefox.
• Copy the two files (.part and 0 byte final) that you moved above back to the download location to replace the new files that were created.
• Resume the download in Firefox.