le David Adler (Forbróir) ar Beal. 27, 2012 · buan-nasc

This usually happens when the image is slow to load (and it'll finish eventually) or has an connection error when it's partly loaded. Do any messages appear in the 'Errors' tab of Tools > Developer Tools > Error Console?

You could try pressing 't' to load it in a new tab and see if Firefox is able to load it without Thumbnail Zoom Plus.

The next major release of TZP (2.0.0) will update the display more often while loading which will help if the image is just slow to load.

You can follow-up to firefox.add.on@davidadler.name .