Hi, thanks for the replies !
Interesting to say, that two hours ago the website did cause high cpu, and now it does not.
It did that even with minimized Opera. But I think, Opera got a small update meanwhile - it is now 50.0.2762.58, and maybe it was a lower number after the comma before.
The snapshot I saved does take an unusal long time to load, about 15 seconds, which is considerably longer than loading it online . But after loading, CPU goes down to normal.
I'm on Win10/64 with an i7-6820HQ w 16GB RAM/512GB NVME SSD, DSL 20, no Java installed, but of course some other things like Flash. I have set up this machine recently, and the possibility of PUPs is rather low. But there are no gaming clients, nor any Skype or similiar clients. I tend to have a slim system, because I need most of its power for music production, where heavy background process can cause audio problems.
However, On Win10, it's not so easy anymore to 'know your tasks', since MS intruduced a lot of new processes and services. They even change service names and structures sometimes to hinder people on disabling them - best example is the user experience, which is clearly very important to the company.

So for the problem, it seems to be gone for now. Wether it was caused by an AD, a script on the site, or an intruder who read my CPU cache via a hidden Ad script, or simply an element in the ads that was hard to render, we won't know.

Hi, today I started Opera with the session from yesterday,
The CPU-fan of my laptop (i7-6820HQ with Intel 530) started then, and I saw in procexp that one Opera process uses 25% of all CPU. I looked through the tabs, and found the culprit:
gearslutz.com board.
There is no change if I switch on Opera's adblocker, which I did at first, because I thought of a hidden crypto miner script in the ads.
Gearslutz is, by the way, a well-renowned site (despite its name), and the ads (Thoman etc.) seem serious, too.
Can anyone here find out, why especially this site is eating so much performance ? In Firefox it doesn't.
I can kill the process, but then the tab window shows a message that there is not enough memory to show the page. A reload starts the process anew, with the same behaviour.
I have saved the page for reproducing that. Hope it can.
Btw, I use the plugins "Sidewise", "V7 Sessions" and "Disable Html5 playback", but disabling them didn't change anything.
Also not enabling Turbo mode, or disabling the Tab preview.

I think Opera needs desperately a Master password in case of the OS being hijacked.
That can happen if a Laptop is stolen or someone manages somehow to access the computer by overriding the OS password(s).
There are several methods to gain access to a locked Windows-PC. It seems that only an encrypted harddisk (via Bitlocker or such) is safe, but not everybody does that procedure for some reasons.
I understand from the previous posts, that Opera uses the same password as Windows, or the active user account.
With tools like Bart PE one can reset any User account password on a Windows system harddisk, except for those in a network domain (but maybe even some of them, because they have to be stored locally for offline access).
If I understood it right, Opera will follow any changes of the password, so, a thief or someone who can secretly boot the computer with such a tool and then, after resetting the passwords and logging in, can access all Opera passwords.
It's basically a simple "net user" command as an Administrator.
I may sound a bit paranoid, but Laptops are often stolen or even forgotten/lost.
Since there is a growing demand for passwords, accounts and such, if one of my laptops would end in other hands (without my consent), I would have endless work to do, to change those passwords.
On the other hand, not storing them, is not an option (any more). I would need a special app on my phone or on a separate pda to manage them, and I would soon be busy with entering Username and passwords.