Show an alternative icon for features that are blocked and not broken.
Tor Browser blocks certain features, and especially so if the user is using the the highest security setting. Currently, there is nothing distinguishing elements on a page which were legitimately broken versus ones that were blocked.
Instead of the broken image icon, it would be ideal to have another icon (onion icon?) there instead if it was blocked, to indicate that it's not broken, and Tor Browser is working as intended. Adding a popup on hover or click to describe why it was blocked would be even better! I've mocked this up below.