That combination should certainly work, and does for me. Try restarting your computer and try disabling all your other Safari extensions if you haven't yet.
It's perfectly safe (the main change from the release version is this fix), it has no effect on your data, and you can uninstall it or switch back to the release version immediately (though there's not much point switching back to a broken version). We'll release it sooner if you can confirm that it fixes the problem for you.
version => 5.0.47, platform => MacIntel, oscpu => Intel Mac OS X 10.13, locale => it-IT, appName => Zotero, appVersion => 5.0.47, extensions => Zotero LibreOffice Integration (5.0.13.SA.5.0.47, extension), Zotero Word for Mac Integration (5.0.15.SA.5.0.47, extension)
Can you install this beta build and confirm that it fixes things for you?