My wife and I just spent 15 minutes looking for the Clear Cache option in Firefox. We actually had to google the SuMo article to find where this option is hiding. We both had the association that cache has to do with the content that is cached. We never actually thought we'd find this under the Advanced/Networking tab. Moreover, the article, and other search results, don't at all mention the History/Clear Recent History option which, after doing some clicking around, can do the same thing. Would it not make more sense for this option to be placed under the Contents preference tab rather than the Networking one under Advanced? NI'ing :phlsa as suggested by :gijs.
Advanced/Networking seems about right to me. The average user shouldn't have to deal with this; the preferences under Content seem more end user facing.
Agreeing with Dão here. That said, it sounds like the SUMO article should really mention clear history (if that actually clears the cache as well) in that context.