Got the same problem. Not been able to fix. I was asked to test in safe mode but it did just the same.

I unistalled Firefox Clicked the delete all data.

Do a backup of bookmarks first.

then reinstalled Firefox.

Seems to work ok. I can download my attachments now.

I uninstalled Firefox, deleted all data, reinstalled and still have the same problem. I guess I'll go back to Internet Explorer.

Make sure that your security software isn't causing these issue in case they scan the file before allowing the uploading or otherwise block the files.

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

Firefox 30 will not upload or download any files. This happened all of a sudden. I have done everything to troubleshoot from ad ons to virus scan and reset Firefox. IE works OK...so I know it's a Firefox issue.

Did you check the advanced settings for Firefox your security software (firewall, anti-virus)?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

Did you try uninstall, click delete all data, then re-install? That worked for me. I have 29 though. I had tried the safe mode, blah blah blah that the techs told me to try.

here is link to my question https://support.mozilla.org/en-US/questions/1001913?esab=a&s=&r=0&as=s