1. Enter about:crashes in the Firefox location bar (that's where you enter your website names) and press Enter. You should now see a list of submitted crash reports.
2. Copy the most recent 5 report IDs that you see in the crash report window and paste them into your forum response.

More information and further troubleshooting steps can be found in the Troubleshoot Firefox crashes (closing or quitting unexpectedly) article.

It is possible that your anti-virus software is corrupting the downloaded files or otherwise interfering with downloading files.
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

download problem not in safe mode !!!

Have you tried to Reset Firefox? Refresh Firefox - reset add-ons and settings

Is that Firefox safe mode or Windows safe mode?

If it does work in Firefox Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe Mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")