Weird Safari behaviour!

[Gij8708]

Hi,

Today safari (v11.1) on Mac HighSierra 10.13.4, started to behave like crazy. For some reasons, this is the resolution I get every time I open the browser.
It looks a kind of mobile resolution. I restarted, erased the history, changed from view --> font in, font out, but nothing happens.
I attach 2 screenshots, the most interesting is the google search.

What should I do? Now I am writing from Chrome and it works ok.

 

[Gij8708]

Any help? I also checked develop → User Agent and check if it's set to default. When I switch to some options, it reloads correctly and then goes back to the same view.

 

[Gij8708]

Please can someone help? I am desperate. I cannot surf anymore.