Implementing Boomerang into a browser extension/plugin

I am currently developing a browser extension/plugin that one would install and would then report information such as page load times, number of objects on each page, etc. to a server so that the data could be analyzed.

I was curious if something like Yahoo's Boomerang JavaScript code (http://hacks.bluesmoon.info/boomerang/doc/) would be able to be able to do this. From what I have read, it seems like Boomerang was developed for developers to implement into their own website in order to gather data, but would I be able to gather the same kind of data by putting this code in a browser extension in order to gather the data from each website that is visited?

I don't see why not from a technical perspective, at least in Firefox and Chrome. However, user privacy issues and policies of the browser extension stores might prevent you from tracking users in certain ways and/or without consent. So better check that first to avoid surprises later.

1. You'd need a way to gather information. Judging from your question text, the regular DOM APIs and the PerformanceTiming API might be sufficient. And that's probably what Boomerang uses already. You'd just attach your code (or Boomerang) with e.g. Firefox Add-on SDK PageMod or Chrome extension Content Scripts.
2. You'll also need to transmit the data somewhere. Both Firefox (XUL¹, Add-on SDK) and Chrome extensions allow cross-origin XHR.

So there you are. ;)

¹ XUL overlay scripts are privileged, and not restricted by the same-origin policy.