If you don't see the thumbnails after install try number 1.
- In Windows Explorer click Tools and select Folder options.
Click on the View tab
Expand Files and Folders
Removed the check mark from Always show icons, never thumbnails.
Click the Apply button.
If the above does not work, then do 2
- Right click an .svg file and select properties.
Where it says: Opens With, click the change button.
You may have to select the other Programs plus sign
to reveal and select Windows photo viewer.
Then select OK.
By the way, if you want to open a .svg file with Windows Photo Viewer,
make sure you follow step 2.
Step 1 may be all that is necessary to get the thumbnails to work, you may want to try this prior to installing .svg Explorer Extension.
Hope This Helps.