Hello,
It looks like you are trying to import HTML file using a wrong import field (one that accepts only JSON file type).
Try to use the import field under the "Chrome bookmarks / Opera bookmarks (speed dial)".
That should be able to handle HTML file.
If it still doesn't work, please contact me to my support email (admin@fastaddons.com) with more details - specifically, how was the HTML file created.
Best Regards,
Juraj Mäsiar