So what exactly do you need help with? Is it seeing the files? Or do you want to delete them to recover some hard drive space?

First thing to do is to use a location you choose and may manage yourself. Multiple locations if that helps. The locations may be change din the settings options. See

• Startup, home page, tabs, and download settings_downloads
• Where to find and manage downloaded files in Firefox

Can you give more background information about what it its you are doing.

• Is this something more than just ordinary web browsing ?
• What type of files are these usually ?
  • e.g. .html webpages; .pdf or say .odt documents; pictures, music or videos; applications, binary files, large databases, etc.
• Is this for some one off project or something you will do on a regular basis ?
• For what sort of time period do you expect to need and keep these files for ?
  • e.g. one-off use, firefox session only, a day or less; a longer period days, weeks, months, years ?

The location you are using is for temporary files as indicated by the location name.

The decision may partly depend on how much hard disk space you have. If you have terrabyte storage space you may not wish to store everything you can stream but will not need to worry about a few downloads per day. So some idea of the storage and download sizes helps

• Disk drive, total size, total freespace, Freespace as % of total
• Is this a single disk drive computer ? do you use any other storage besides this ?
• Any idea of how much you "download" each week, and how much if any of that is likely to be kept for a lot longer than a week ?

Firefox caches some information but that will be a slightly different issue.

• Settings for privacy, browsing history and do-not-track
• Delete browsing, search and download history on Firefox

I want to delete these files but cannot find them.

Often using the firefox download manager and right clicking will give you the option to open the file location, if they are nor showing up when you do that they may have been moved or deleted. Did you read

• Startup, home page, tabs, and download settings_downloads
• Where to find and manage downloaded files in Firefox

Otherwise just open the location and search for them. It obviously helps if you know the names of the files. Note that by default the location is likely to be hidden. Also note that some files in the location may actually be useful so do take care not to just blindly delete the full content. One reason Windows may hide files is so that they are not accidentally deleted. For explanations on how to display hidden folders and files see:

• http://kb.mozillazine.org/Show_hidden_files_and_folders
• http://windows.microsoft.com/en-us/windows/show-hidden-files#show-hidden-files=windows-7

I am not sure I understand

 I can't find these files and they are using up space on my hard drive. 

How can you say the files are using up space on your hard drive if you are not able to find them ?

Maybe they were already deleted or over-written and that is why you are no longer able to find them.

If your problem is with disk space then answering the questions I asked previously may help us to understand the problem and its magnitude.

@Snowy19: Try to do this:

1. Goto Start Menu > All Programs > Accessories > System Tools > Disk Clean up
2. Select Drive where your "AppData>Local>Temp " is. This will generally be the Drive in which you install Windows, so it's most likely C: (If you are using Win 7, which I am assuming you are, you'll see the windows logo beside the drive letter in the drop down menu.
3. Select the 'Temporary Internet Files' and the 'Temporary Files' checkboxes. One way to confirm it will be to see how much space they are occupying, if it is indeed quite a lot, then you're on the right track! If you want to view the files, you can also click on the 'View Files' Button in the 'Description' Pane.
4. Select OK to delete these files and free up your space!

Let me know if that worked. If it didn't we'll think of some other way to sort this out.

And I agree with what John99 has said, check his post to configure Firefox to manage the Downloads so that a similar situation does not arise.

Cheers!