I noticed this issue a couple days ago. Using this page as an example: Slickdeals EDIT: Mods over at Slickdeals edited this post because it didn't fit the rules. Also, the OP's link broke, so no attached images. The second and fourth images (from left to right) are PNGs. The second image does not display anything (because the text is black and all whitespace is black), while the fourth image only shows red/orange arrows and what's contained within. I've also found a couple PNGs on my computer don't display properly in IrfanView, but display just fine in Windows Photo Viewer. Also, while the thumbnails of those images display properly in Firefox, when saved to my computer the thumbnails show how IrfanView will display them. If I highlight the image that is completely black (second image), it accents the text in the thumbnail. So far I've tried: Running Firefox without add-ons. Rebuilding the Icon Cache. Changing the default image viewer for PNGs from IrfanView to Windows Photo Viewer. Thanks in advance. EDIT: Added screenshot.