Hmm ... it should work that way now. In fact, only admin users can force a page to refresh its cached content.
Though we are getting a spike in traffic with the redesign launch, New Relic still reports app server response times of <600ms. But WebPagetest confirms really slow load times. [1]
If anyone finds some gross offenders of page performance, please file a bug: http://bugzilla.mozilla.org/form.mdn or better yet - send a pull request: https://github.com/mozilla/kuma !