If you’re running a Plone 4.3.x (and earlier) site, you might have found Google Webmaster tools complaining about mobile friendliness. On inspection, most of that comes from one single template, image_view_fullscreen.pt
That’s the one that displays images in their original format when clicked upon, like News images. Many sites will have their own lightbox or jquery popup anyway, but the googlebot still finds the original link.
It takes three lines to fix this. There’s a pull request already, https://github.com/plone/Products.CMFPlone/pull/407 (UPDATE: merged already, thanks Nathan) but if you’re a site administrator you can also change this one in the ZMI. (It’s under ‘portal_skins’, ‘plone-content’, from there you can customize).
Of course, if you have a theme-product it’s better to override in there, but if you’re not that advanced, you can just use the ‘custom’ folder. I won’t tell ;-)
You do want to address this, as Google will deduct karma points for mobile users.