Comment # 10 on bug 4368 from Kevin Kofler

(Sorry for yet another post, but I forgot something important:)

Just a note of warning: If you want to try out qt5-qtwebengine-freeworld, you
will have to close any running QupZilla instances (from before you installed
the package) and start a new one. Starting a new QupZilla instance next to one
that was already running before installing the package is not sufficient,
because it will reuse processes and thus spawn even the new render processes
with the wrong libraries. If you close all QupZilla instances completely and
start a new one, it works. (If in doubt, just restart the whole session.)

This problem is of course only a one-time problem when initially installing the
package. Once you have the package, it becomes a non-issue.