Hi Henri,
Nice job, you are close to the point where it becomes interesting.
In the left bottom of the task manager there is a knob "Monitor de recursos.." click on it and you get a new screen, select tab "Survey". In the right column of the next screen you will see graphs of the usage of CPU, disk, network and memory.
If you can look on that screen on the moments you get those blank/flashing screens we may find out which resource is short.
You can also see whether opening and closing the browser with all those tabs make any difference.
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Leiderdorp
Yes there I live, a village just outside a small city of Leiden. It is the place to be when you like a real Dutch scenery with rivers, mills and lakes and Leiden with its old university has so much history.
If you are not interested in history stop reading here, but I really must tell it:
Leiden the birthplace of Rembrant, later he moved to Amsterdam; Jan Steen another old Dutch master lived and worked here.
Prof Lorentz lived and worked here, his work was an inspiration for Einstein, he got a Nobel prize for his work.
Prof Kamerlingh Onnes was the first who was able to make liquid helium, close to 0 Kelvin, those days it was the coldest place on earth, with it he discovered superconducting, he also got a Nobel price.
Paul Eherenfest lived and worked here, quantum mechanics, friend of Einsten who often stayed with him in Leiden.
Prof De Sitter also from Leiden, had the famous debate with Einstein about the cosmological constant in the general relativity theory, De Sitter was right, the universe is expanding.
(There goes a story that Einstein once applied for a position at the university in Leiden, he never got an answer, they were looking for a researcher not a theoretician.....)
There is a great collection in Museum Boerhaave of those remarkable scientists:
Overzicht - English Museum Boerhaave.
Boerhaave itself was a famous doctor, one of his students “Van Swieten" was the doctor who cured Maria Theresia of Austria of childlessness.
To much history, I behave like a child in a candy shop, but where do you live?
Henk