I just read Taras' great blog post Extensions & Startup and it got me thinking that we should just automate this and advertise it with extension listings at addons.mozilla.org.
All you'd need to do is have some automation that gets triggered when an AMO editor approves an extension that measures its impact on startup and publishes that as a required part of the extension's description in the gallery.
That way users could evaluate that against their desire for fast Firefox launch time and make informed decisions about which add-ons they're going to use.
This might also inspire extension authors to consider focusing more on ameliorating start-up impact through various techniques like delayed loading.
