In lieu of this new information, I wholly agree with you.
You said that using the mydlink website generates the same artifacts? Did you try using mydlink from different PCs (or has your testing been confined to one PC)? (Lets put mobile devices aside for now).
Now I've tried these:
1. Laptop Win7 64bit IE FF GC Java32+64 7.4
2. Desktop WinXP 32bit IE FF GC Java 7.4
3. Desktop Win7 64bit IE FF GC Java32+64 7.4
This was ok at first with a fresh install of Win7 with Java 6.29.
But after upgrade to Java 6.31 it's broken.
Even after restore to a point before Java. Now it has Java 7.4
I have not deliberately changed anything in Java config, but anyhow I think the problem is related to Java.
The picture is only a lot of colors like a coded transmission. Impossible to see what it is.
4. Laptop Win7 32bit FF Java 6.31 ok
This is the only one that's ok now.
I don't dare to upgrade Java on it