I did say "sandboxed", did I not? Just have your VM refuse to download anything before you click somewhere, and let it compute the relevant URL so it can show

I did say "sandboxed", did I not? Just have your VM refuse to download anything before you click somewhere, and let it compute the relevant URL so it can show it to you the way Firefox does. If this is too harsh, then relax the restriction to only download to, say, the domain name of the current main URL. If this is still too harsh, then have a NoScript like button to relax restrictions manually, on a case by case basis. It would disable any form of cross scripting by default, which in my opinion is a better state of affairs than HTML alone is right now (now, you can embed an external image in a web page, and bam, Facebook knows what you read).