Thank you very much Carl! That was a good tip.
Grid works fine as long as you can live with a fixed number of columns. Usually my gallery should re-arrange the thumbnails when resizing the browsers window.
I am pretty sure to have tried several style options like gallery and subgallery (unfortunatelly ignoring grid), with no success. Working on a different computer, thus using a different browser, the gallery suddenly displayed perfectly using the style 'gallery'! Even when resizing the browser.
So it has been a problem with my browser Iceweasel!!! :-( (I have to admit, it is a bit outdated...)
Although I don't know why Iceweasel is not showing the gallery in the desired way, I now know that I did everything right :-)
Yours Marco
You should be able to change the view style to grid under Basic settings and adjust the number of columns.