The methodology is questionable on several fronts:
- you can't use the load event to compare advert-heavy vs. advert-free load times. The load event does not fire when the page is usable by the viewer, it fires when every last request is done, in particular even requests fired from various advert iframes. However, those requests may not impact page usability. The load event may even never fire - any offscreen 1px spacer gif that times out will cause that! I don't think there is a built-in event for "done-enough", but the load event is certainly misleading.
- opening the developer tools causes various side-effects; those can cause the page to load more slowly than usual. You shouldn't benchmark with developer tools open (unless you're explicitly targeting usage with devtools open...)
- comparing load times across browsers as reported by the browsers themselves may be valid, but it's not obvious. You definitely want to check that carefully.
- Measuring "peak" CPU usage is almost meaningless without considering how long the CPU is used.
- Measuring the chrome extension process CPU usage and memory usage isn't very helpful, because running this kind of extension causes CPU usage and memory usage in every content tab. Both of these statistics for chrome in this use-case are meaningless. You'd need to measure the memory usage and CPU-time of the entire chrome process tree to get meaningful results. Even in Firefox without e10s it's not valid to measure just the main process CPU and memory usage because plugins are in separate processes (and things like flash or h264 decoding can definitely use CPU and memory).
The only thing this page really makes a decent case for is that Chrome loads pages faster than Firefox - but even there, it's not clear we're dealing with an apples-to-apples comparison.
Running WPRUI with first level triage will measure CPU along with a bunch of other stuff. Enabling ReferenceSet under memory Resource Analysis will measure memory usage.
Chrome has an ETW provider, I poked around a bit and couldn't find any for FF (it looks like they register one for the JS engine?)
I'm not familiar with how to solve the "page loaded enough but not done" problem, but IMO if you measure end-to-end times it's probably a close-enough proxy. Maybe measure several times and report on those statistics.
(Edit: Taking a trace with/without the adblocker enabled should allow you to exactly count # of sampled cycles spent in the adblocker - easy to compare in WPA, as long as there are events emitted indicating page load start/stop).
(Edit2: Using UIforETW along with Chrome 46+ will let you see ETW events: