What and where are you trying to download? What error messages? What are you using for the download?

http://download.cdn.mozilla.net/pub/mozilla.org/mozilla.org/firefox/releases/

also,

Using another computer, Download Firefox Full Version For All languages And Systems {web link} onto a thumb drive. After, plug the thumb into your system.

Try this:

• Download the Firefox installer and save the file to the desktop
  https://www.mozilla.org/en-US/firefox/all/
• Start the installation with a double-click on the desktop icon

It is possible that Anti-Virus security software is causing problems. Try to disable Anti-Virus security software temporarily to see if that makes a difference.

jimdover said

I've tried 3 different downloads. Firefox seems to be stuck.

It was Malwarebytes Premium that was blocking the download. I had to create an exception.