I can't believe there is no way to disable this annoyance now apart from downgrading.
I used the following link to suggest an improvement:
https://opera.atlassian.net/servicedesk/customer/portal/9
In Opera Settings, on the left, there is a "Rate Opera" link which I used to tell whoever receives it how pathetic this "feature" is. Best thing is it can be used multiple times.
Maybe if they get a few hundred negative comments, they'll start considering adding two lines in their code so we can Disable this Unwanted crap.
But then again, there is no limit to devs arrogance.
Remember devs, having a tabbed browser is useful for having Multiple tabs. That means that having 10+ tabs opened is not a rarity. Your tabs tooltip is Not a good thing in that case. Find another way to implement it or let us disable it.