> What if there was a mechanism for signing a webpage? > This could easily be promoted as a safety feature, you only run the code the web server gives you, not something that has been exposed to a man in the middle attack several times over.

This already exists, it is called https. The s in https stands for security, i.e. encryption and signing.

> The browser could be told not to render anything is the signature does not match the content.

The problem with this statement is that adblockers are part of "The browser". So the browser/the adblocker coud still choose to render something with no signature. Also, what does "rendering" mean? An adblocker changes what "rendering" means: For example, if the html includes the line <img src="https://www.qries.com/images/banner_logo.png" alt="Qries" width="200" height="90"> then the browser will usually request banner_logo.png and show that here. But the browser could also choose not to do that. If qries.com would be in the blocklist of your adblocker, your browser would choose not to send that request and not to show that image.