When I go to "file -> save as" in the menu of FireFox, I get to name the main file and choose path.
The extension is default .htm and any additional files will be stored in a folder in the same path as the main .htm.
See attached screenshot of the saved file(s). I chose the name Wire" in this case.
When I imported the .htm, the belonging folder did not tag along, so I manually put it into the same place/folder as "Calibre" stored the imported file.
This worked as a charm, and I guess, since it did work, I'll continue do the .htm(l) file import and convert the same way.
I can always delet the .htm(l) with the related file folder if I want, after a successfull conversion
