, if you don't have thumbnail feature switched on, the folder containing your photos will appear as a list. If you see mini photos, then you have thumbnails switched on.
I have used the function mode to Thumbnail mode
This is not a generic switch to enable thumbnail viewing, but instead switches on thumbnails for the particular folder you are in at the time (just like delete doesn't delete all but only the file you have selected).
let's say you have two subfolders in your images folder 'Cats' & 'Dogs'.
If you want thumbnails in both folders, you have to use function mode twice (once in each folder) to create the file thumbnail.tvix
in each folder.
I imagine that your thousands of photos will be over many more folders, so if you want thumbnails in every folder, here's an easier way to do it...
Connect TViX to your computer via USB
Browse to the first folder you want thumbnails in
Create a file called thumbnail.tvix
Now go the the next folder and do the same
Continue doing this until each folder that requires thumbnails contains a copy of that file
NOTE: Function mode is not an ON/OFF switch. To stop using thumbnails in a folder, you have to physically remove the thumbnail.tvix file via a USB connection
I hope this helps