There are a range of different kinds of forms. For example, this site uses very simple controls that don't automatically convert Word's formatting to an online format. The site where you are trying to paste your resume probably works differently.

What methods have you tried using to paste? Typically one of these will work:

• Ctrl+v
• right-click > Paste
• Edit > Paste (from the menu)

Some sites offer their own buttons to paste, but for security/privacy reasons, Firefox usually disables those.

This is going to sound random, but if you haven't shut down and restarted Windows since this problem started, you might want to try that. Some shared facility in memory might be corrupted.

My computer went through an unexpected restart for maintenance yesterday morning after a regularly scheduled one just a few days earlier, so I didn't think to restart it again, but it worked! So simple and not random at all. Thanks!

Great answer. You just saved my HP from learning to pass through walls.