Necrobump!
I am also having this very same problem, running Firefox 3.0.14 on Ubuntu 9.04. I can view images on different machines on my network, and I've just downloaded some browser I've never even heard of before - 'Epiphany' for Ubuntu - and that works just fine.
The images plainly are available but I can't get to them - anyone know of a fix for this? Something to tweak in about:config perhaps.
Cheers!