I wrote an add-on for Firefox 4 that tracks how long various parts of the browser's user-interface take to load. It does not require a restart of the browser.
- It measures the duration between 'popupshowing' and 'popupshown' events. This covers menus, menu-like things, and those floating panels you're starting to see everywhere.
- You can see your results at about:response. There won't be anything there if you just installed the add-on. Browse around for a few days and then check it out.
- It doesn't track popups without an id yet. It could also be nicer by showing the containing menu name if available.
- I'd like to add window load times. What else in the front-end could we be measuring? I was thinking about <command> execution, but there's not a way to do that without modifying the core, afaict.
- Perhaps we could add a button for users to submit their anonymized data somewhere.
Try it out, let me know if you have any problems. The source code is available on Github.