It's the 5,6,7,8 version you need ...
When Software Installer had installed it and the dependencies I could only start Opera by either changing the Preferred Application for Browser to Opera or by typing 'opera' in a terminal - ie it didn't show up in the 'Connect' section.
I saw that 'opera.desktop' was in usr/local/share/applications rather than /usr/share/applications as the rest of the apps are, so I copied it to /usr/share/applications (had to be su to do that) and then added this line to /home/user/.config/xfce4/desktop/group-app.xml:
<app sequence="x">/usr/share/applications/opera.desktop</app>
(replace x by your required location of the Opera 'O')
though I could have changed the line to .../usr/local/share/applications/opera.desktop... and not copied the file I suppose.
This added the icon, but started Opera with the %u error - fixed by changing the line Exec=opera %u to Exec=opera in opera.desktop (opened in Mousepad, changed the line, saved the file again).
HTH.