Is it just me or is it not obvious that this entry actually does something useful instead of duplicating the OS screenshot feature? An image of the entire page including the part not on screen isn't even a screen-shot.

Yes! Me too and so when a site hijacks right click it's a little infuriating (but I have now learnt the keyboard shortcut).

Also I think holding shift while right-clicking will show the context menu even if the site hijacks right click. (And for some sites, I'm pretty happy with a custom context menu, so it's good to have both available.)