I tried it and visited css-tricks.com and when using the 'Live HTTP Headers' it still makes the request to Google with the referer. However, the Firebug net inspection appears to locally load it (0ms load time).
> submitted a Firefox addon for approval a few years back that introduced a separate cache for all the AJAX libs, but it was rejected for silly reasons
I have actually been looking for such an addon. I too clear cookies/cache/etc on exit in addition to using NoScript and a strict Adblock Edge (block social networks/tracking/not just ads). The only area remaining to be fixed would be the AJAX libs to be hosted locally.
Would you consider making a github page or something so you can provide the addon without being in the firefox addon explorer?