Can you elaborate?
> I have frequent crashes, it’s slow at rendering pages, it uses more memory than (for example) chromium and seems to leak memory; any kind of CSS animation causes the CPU to have a major workout.
Those are indeed most likely caused by the underlying QtWebEngine in some way - though there also have been some performance improvements in qutebrowser itself, with some more planned: https://github.com/qutebrowser/qutebrowser/issues?q=is%3Aope...
> After one upgrade most video stopped working.
If you installed qutebrowser outside of Ubuntu's packages, that might be caused by the prebuilt Qt lacking proprietary codec support.
Despite that, it's what I'd recommend if you're on a Ubuntu LTS with often grossly outdated Qt versions: https://github.com/qutebrowser/qutebrowser/blob/master/doc/i...
> I never cared about the ad blocker, as I use a hosts file for that. Why doesn’t everyone? It seems to be a better solution.
That's essentially what qutebrowser did before this release as well - but many ads and trackers are served from the visited page directly rather than a third-party host.