Lags when scrolling a large page

[SafaAlfulaij]

Opening this page: https://github.com/QupZilla/qupzilla/blob/master/src/lib/webkit/jsalert.ui
and trying to scroll it make the application a little laggy. The fan start spinning and stopes when I stop scrolling.
Maybe it's a Qt problem?

[SafaAlfulaij]

Dublicate #1445

[pejakm]

@SafaAlfulaij As you noticed yourself, this has already been reported to us and upstream, so we will track #1445.