QupZilla-1.4.4 $ grep qtsingleapplication src/lib/lib.pro include(3rdparty/qtsingleapplication.pri)
The qtsingleapplication.h in QupZilla package is not the same with the one in the portage. I doubt whether it is the correct thing to do.
See also: https://github.com/QupZilla/qupzilla/issues/1503
(In reply to Coacher from comment #2) > See also: https://github.com/QupZilla/qupzilla/issues/1503 wrt qftp for qt5, I tried to package it some time ago but it failed to build.
(In reply to Coacher from comment #2) > See also: https://github.com/QupZilla/qupzilla/issues/1503 As can be seen from the discussion there, upstream is receptive, but the issue has not been resolved yet. We currently cannot use the unbundled system package, since QupZilla uses a patched version. I'm keeping this open in the hope that a future release will make it possible to use system QtSingleApplication.
According to upstream, it's not possible to use the system copy due to their custom modifications.