How to make the Windows XP explorer window open files in a webdav folder on double-click

When I open a local file folder in Windows XP explorer, I can right-click on any file and see a context-dependent set of actions that can be performed on that file (Open, Edit, Print, etc.) The one highlighted at the top is what is executed when I double-click. However, when I browse a web folder, most of these actions are missing, and what is more, the "Folder Options" panel (under tools) is missing the "File Types" tab where I am used to configuring this sort of thing. What gives?!?

Background
Doing a google search revealed a related problem encountered by users who have upgraded to Vista. Apparently the Vista developers decided to remove the "File Types" tab from the "Folder Options" panel of Windows Explorer. I guess a lot of that functionality, but not all, has been provided in a new control panel widget called Default File Types or something like that. Regardless, it has a lot of new Vista users up in arms and looking for ways to get back the power to directly manipulate the context menu for particular file types. Reading through this discussion eventually landed me on a path to discovering where my action items had gone in Windows XP.

Explanation
The answer is that explorer treats the files in a web folder differently from local files. A web folder is a directory on a web server that supports the webdav protocol. One opens a web folder in Windows XP by using Network Places/Add a Network Place and giving a URL in the place where one would usually type the \\servername\folder\path to a windows share. Windows XP explorer displays file and folders in a web folder using icons that correspond to the filename extention, the same way as they would be displayed in a local folder. However the context menu shows a reduced set of actions and double clicking produces a different result, most often nothing! The reason for this is that most applications cannot handle a URL the way they would accept the pathname to a local file or one on a mounted network share. Unless an application is able to open files whose pathname begins with http: or https:, the action items associated with that application are suppressed when the icon is displayed in a web folder window of explorer.

Resolution
So how does Windows explorer determine whether or not an application is able to open files based on a URL? Inside the registry is a table of registered applications found under the key \HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft \Windows\CurrentVersion\App Paths\. Any application that is able to open a type of file that is registered with explorer should be in that list. If the application is able to open a URL should have a special entry under its key name "useURL". The type of the entry is "string" and its value is "1". Of course, this should only be present for applications that actually are able to open files over http or https protocols. Adding this as a String value to the key for firefox made the Open actions for many of the files in my web folder suddenly accessible with a double-click action.