Thanks for the bug report, and indeed qbittorrent web ui does not work in firefox.
But it does work in Chromium, Iceweasel, and Midori. So it seems like an issue with the official Firefox package. The samw deps are loaded and available for all three browsers so it is not a dep file issue, but qbittorrent does not want to work with Firefox.
In this case, it is recommended to use the other browsers for qbittorrent.