refer to

• Applications panel - Set how Firefox handles different types of files

and if that fails, delete the mimetypes.rdf file in the profile folder.

• http://kb.mozillazine.org/MimeTypes.rdf#Deleting

To go to the profile folder.

1. Go to FIrefox => help => Troubleshooting Info
2. Hit the open diretory button (or wording similar to that).
3. When the file manager loads, close firefox then delete mimetypes.rdf

Are you trying to access your downloaded files from within Firefox, by clicking on the toolbar arrow and then selecting "Show All Downloads"? Ref: Where to find and manage downloaded files in Firefox (under How do I access my downloads?).

Do you see your zip files listed in the Library window? If so, then you should be able to open them unless you moved them to another location after downloading. The Firefox Library window will only let you open the file or the containing folder if it is still in the original location.

Try searching on one of the file names to see where it's located. See http://windows.microsoft.com/en-us/windows7/find-a-file-or-folder Once you find your zipped files, you should be able to open them in Windows Explorer. See http://windows.microsoft.com/en-us/windows7/compress-and-uncompress-files-zip-files

It shouldn't be a problem to open ZIP archives in Windows Explorer with a double-click or via the right-click context menu, just like you would open a normal folder.

You can find "Open containing folder" and Open in the right-click context menu of an item in the Download Manager (Download button on Navigation Toolbar: Show All Downloads)

Firefox manages downloads in the Downloads folder in the Library (History > Show All History)

• Downloads are treated as history items: clearing history removes included download items and vice verse.
• When downloads are in progress you see an animated download button on the Navigation Toolbar showing an estimate of the remaining time
• The Download button gets a green highlight once all download are finished to make you aware that new downloads are available.
• Pause and Resume can be found in the right-click context menu of an item.

You can display the new Download Manager in a tab by opening the about:downloads page and consider to open this page in a separate window.