In chrome, when you right click on an image, there is a popup menu contains find similar images. Here is not. It is good to have.
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.
I think such functions are the role of extensions.
As an example of an add-on for this:
If you prefer Google Image search, someone probably created an add-on for them, too.