Is there a way to make anyone accessing my home wifi network get this injected into their webpages (or random webpages)? I know there is that trick that lets you flip all the images or replace them with pics of something else (usually cats) but can you inject arbitrary js into pages also?
I think you'd need a proxy server that injects the JS into each page. Then your network's DNS should redirect to the proxy.
edit : port 9999 edit 2 : port 9990