In the final 1.8.0 version (build 1070), you can disable ViewList thumbnails with the following command from the Process Console:
set MainWindow/ShowViewListImageThumbnails=false
This global flag still isn't accessible from the Preferences interface. It will be available in the next version.
For a list of all configurable global flags, enter this command:
set -lb
For more information on the set command:
help set