The option for choosing the default viewer for images in the associated application is moved to Project Manager menu above the address bar.
Project Manager viewport
Also 3rd version allows viewing any type of asset in a separate window. Whether is it an image, an HDRI file, a 3D FBX file, 3DS, BVH or IES file – any of these files you can view in high resolution in a separate window. The file in the window is updated when you change the file selection in the list. You can also save the selected view for a 3D file into the file’s gallery.
To opening a file in a separate window, find a related option on the menu or use the SPACEBAR key.