Now both nsIContentPolicy and on-http-* observers are used for net request
monitoring.
Reasons:
- In many cases, nsIContentPolicy.shouldLoad is invoked twice for the same
resource, because of the speculative parsing.
- nsIContentPolicy.shouldLoad don't have information about the channel,
so it can't redirect the request, nor change its headers, however
on-http-opening-request can.
Also, local mirroring and inline-script blocking has been implemented.
Initializing the extension with AddonManager takes too long (at least for
this extension).
When starting the browser, tabs loaded before the extension could, and
because of that, blocking didn't work.
It works better, if it's initialized when the window's DOM is ready.
Pass the extension data (name and version) as the fragment of the URL
for the background script, so vAPI.app can be filled without using XHR
to read the manifest files.
