Ask HN: Best way to anonymize connection from a browser extension?

At Blippex (https://www.blippex.org ) we use browser extensions to collect the URLs and time spent on pages to feed our crawler for the search engine.

We don't want to know who sent this data, it should be as much anonymized as possible (we don't want to know the IP address, the browser, nothing, just the URL and the time spent), but what is the best solution for doing this?

I don't think it is possible to implement a Tor-client in Javascript, and including some shady proxy-server-lists is maybe not the best solution. We thought already about building up a P2P network, but not sure if possible as an extension, any other ideas?