I spent few hours till I found reason why my image (gravatar) looks blurred on WordPress page. I tried to change CSS, upgrade FireFox, set bigger gravatar … In short, the reason was page zoom. After Zoom Reset, images were displayed normally. You can find zoom reset in FireFox menu:
# go to the FireFox menu and make zoom reset View -> Zoom -> Reset # or you can use shortcut (press control + zero) Ctrl + 0
As you know, in FireFox and IE you can control page zoom by holding Ctrl key and turning mouse wheel back and forward. But if you leave Zoom Text Only unchecked, FireFox will zoom and images too. This is nice feature, but images with exact size will become blurred on HTML page. So, if you want to prevent that behaviour, go to the FireFox’s View menu and check Zoom Text Only:
View -> Zoom -> Zoom Text Only
I hope this tip will save your time.