It doesn't. I have heard of this firefox feature before, but never been able to get it to work successfully. On the other hand, if you just type "webkit" in the address bar of firefox or chrome, the google search results contain a link to the relevant wikipedia page on the first page of results. Given what I have to assume is a vanishingly small proportion of firefox users who are even aware of this feature, I don't think the feature is important enough to justify a design decision this big.