Debian 9.6 with KDE.

If I click link from Twitter client Choqok, it make file like "14588_0_jCMIcrXTh7" or something like that to /var/tmp and tries to open it with eBook reader Calibre. File contains HTML. If I click that file, Firefox will open it.
I've checked file type options and it should open default with Firefox. Can't understand why it tries open it with Calibre E-book editor.

Calibre E-book editor gives error:

calibre, version 3.31.0
ERROR: Unsupported format: Tweaking is only supported for books in the AZW3 and EPUB formats. Convert your book to one of these formats first.