Hello, I think the issue for me is, that with libqt5core5a 5.15.2+dfsg-5 the qbittorrent-nox reports this content type:
content-type: text/html while with version 5.15.2+dfsg-7 it reports the following content type: content-type: application/x-extension-html and firefox instead of displaying the web page, it offers to download it.