I click on a product and its detail sheet does not open?

Short answer: While a shop is being edited, clicking a selection thumbnail serves only to drag it. To open the detail sheet, click the small (i) icon at the top left of the thumbnail.

Cause

On a shop being edited, the thumbnail of a selection product has one job: being grabbed and dropped into a collection. A plain click is therefore reserved for drag and drop, and opens nothing.

This is not a breakdown, and it is not your browser: the same click, outside edit mode, does open the detail sheet.

Solution

Click the small (i) icon at the top left of the thumbnail. The detail sheet opens, and there you get everything the click does not give you:

changing the colors kept — see How do I choose the colors of a product;
removing the product from your selection;
reading the product details.

Both gestures start from the same thumbnail: hold and drag to drop it into a collection, click the (i) to open the detail sheet. It works the same way as logos, where the thumbnail also serves both purposes.

Going further

How do I add products to my shop — drag and drop, the thumbnail's other use.