Removing file / folder link after using "Save As..." then "Web Page, complete"
Solution 1:
As I discovered, GAThrawn's answer is good if you have Office XP / 2003 installed on your system. If not, you need to jump into the registry;
Go START -> Run, type "regedit" and in the registry editor, browse to;
HKEY_CURRENT_USER -> Software -> Microsoft -> Windows -> CurrentVersion -> Explorer
Right-click in the left panel to create a new DWORD Value. Call it "NoFileFolderConnection" and give it a value of 1.
That's it! If you ever what to turn the linking on again, change NoFileFolderConnection's value to 0.
Alternatively (if you're comfortable applying a registry edit via a downloaded file) you can find a downloadable solution here; http://windowsxp.mvps.org/webpairs.htm.
More information can be found here; http://msdn.microsoft.com/en-us/library/bb776887%28VS.85%29.aspx
Solution 2:
Based on Microsoft's documentation:
Another option which doesn't require registry modifications is simply to rename the HTML file or the folder.
When trying to rename the file/folder, the following message will appear:
Rename Warning! If you rename this file, it will no longer belong to the folder Test_files. To rename it safely, open the file, save it with a new name, and then delete the folder Test_files. Do you want to rename this file anyway?
After approving it, the connection between the html file to the files folder will be removed. Now, you can delete/move the folder. After you've done you can rename the file's name back to its original name.
Solution 3:
@Pavium is right, this is a Windows setting not a Firefox setting that stops you separating the folder from the file easily. Firefox does have an option to save just the HTML page without the associated media ("Save Page As, then select "Web page, HTML only") but it doesn't sound like that's what you're asking about.
To stop Windows linking the file and folder permanently, open up Windows Explorer (not Internet Explorer), click Tools menu, Options, click the View tab, then scroll about halfway down the Advanced Settings box, you should see a "Managing pairs of Web pages and folders" which is probably set to "Show both parts but manage as a single file" at the moment, you probably want to select "Show both parts and manage them individually".