Hi,
This is a known bug :-
and there are two work arounds for this:
File Types Workaround:
1 Open Windows Explorer (Win+E).
2 Go to Tools -> Folder Options -> File Types
3 Select "Extension: (NONE)" and "File Type: HyperText Transfer Protocol".
4 Go to Advanced -> Edit File Type -> Select "open" -> Edit
5 Disable the the DDE message box (which should contain "%1" or something similar).
6 Repeat for "File Type: HyperText Transfer Protocol with Privacy" and any other protocols you want to fix.
Registry Workaround:
Be sure you are familiar with the Registry as this has a chance of corrupting your entire computer system if you bother other registry entries.
1 In Start -> Run, type "regedit" and press Enter.
2 Use the directory tree hierarchy to navigate to "HKEY_CLASSES_ROOT\HTTP\shell\open\ddeexec".
3 Delete the "ddexec" folder.
This info can be found here in the Mozilla Knowledgebase. Hope this helps.
J.