I wanted to try Opera again on my ubuntu (vanilla, i.e. gnome) linux box, but came across an issue just as described here:
https://forums.opera.com/topic/57663/how-do-you-restore-the-standard-title-bar
No direct reply is possible there, as that issue has been "locked" -- without any solution offered.
So it's a pretty old problem but it seems unaddressed.
I'm not going to use one browser instead of another at the cost of having to change my workflow -- which I don't believe would be something any experienced, productive user is prepared to do just on a whim.
So, uninstalled -- and reversed my advice to colleagues to also try Opera.
But I'll keep an eye out on this forum in case anything moves on this matter.