Where did the folder option dialog go in Windows 8 preview?

This is possible. Open up any explorer window then simply click File on the Ribbon, then click on Change folder and search options.

enter image description here

From here, you will get the normal dialog.

For single click opening choose Single-click to open an item (point to select) from the Click items as follows section on the General tab.

enter image description here

To show file extensions, choose Hide extensions for known file types from the big list under Advanced settings on the View tab.

enter image description here

Of course, you can also access it from command line / Run prompt:

control /name Microsoft.FolderOptions

Note that the menu described in the other answer to open folder options from explorer has been removed in the CP.

Related