Is the bad one a normal desktop shortcut that specifies a profile via -P "<profile>" in its target field ? In such a case you can either remove that part or add the -no-remote switch.

• https://wiki.mozilla.org/firefox/CommandLineOptions

Both the good and many of the bad types are files of file type: ‘Firefox HTML Document’ located in sub-folders in the desktop tree and have an associated folder of the same name suffixed by ‘_files’, located in the same folder as the document. Some of the bad type don’t have the associated _files folder. Some have dot extensions on the file name. Correction to the initial question: files, with the good icon, on the remote computer do open correctly. The only consistency is the type of icon.

This may be the clue: Right click > Open With – gives two options for Firefox. The orange one fails both types. The red one opens both types correctly.

Regards, Murray Aikenhead.

What are the file extensions of the good and bad files? If you right-click on a file, choose properties then look at the Type of file section, then what does it say the extensions are? (i.e. what does it say in the brackets?) Do, for example the good ones have file extension .html, whereas the bad ones have a different extension?

Because I am wondering if this is a file association issue, where the good file extensions are associated to open in your normal Firefox with your normal user profile (that has all your bookmarks etc.), whereas the bad file extensions are somehow associated to open Firefox with a different user profile?

Internet shortcuts should always opened with the default browser. This error is more likely to happen if you have already started Firefox with the -no-remote command-line switch, so check possible desktop shortcuts.